We have argued elsewhere that a factory-direct number is mostly a question of what the trade term leaves to you, and that buying wholesale is really a question of time — whether the eighth container matches the first. This piece starts where those ended, at a more basic place: the number itself, and the units it is made of.
We do not publish a price list. That is not modesty and it is not a sales tactic. A system window or a system door is not an object with a price attached; it is a bundle of consumption quantities waiting for a specification to tell them how big they are. Until someone says how many square metres of glass, how many kilograms of profile, how many sets of hardware, which surface treatment and how many identical units, there is nothing to put a number on. A published list would either be a fiction or a trap.
Here is the sentence that matters most in this article. A wholesale price is not a retail price with a discount applied. It is a price in which several of the inputs have been replaced, and the replacement is usually invisible because the unit on the quotation does not change. You are quoted in square metres. Almost nothing inside the factory is counted in square metres.
A published Chinese unit-price analysis sheet for a thermally broken aluminium top-hung window — the kind of document that cost engineers circulate — breaks a single square metre of finished window into separate consumption lines. What is striking is not the amounts, which we will not reproduce, but the units. In one square metre there are square metres of glass, kilograms of aluminium, cartridges of sealant, metres of gasket, fractions of a hardware set, sets of corner brackets and cartridges of foam. Seven of the lines do not share a unit with the total.
| Line in a published unit-price analysis sheet | Unit it is counted in | What physical quantity it actually tracks | Does it dilute as the panel grows? |
|---|---|---|---|
| Insulating glass | Square metre of glass | Glass area, slightly less than the window area | No. Flat per square metre. |
| Thermally broken aluminium profile | Kilogram | Total profile length multiplied by section mass | Yes, and sharply. See the arithmetic below. |
| Sealant | Cartridge | Bead length | Yes |
| Gasket and weatherstrip | Metre | Perimeter | Yes |
| Operating hardware | Set | Number of sashes that actually open | Yes, then it jumps to a higher load class |
| Corner brackets | Set | Number of corners | Roughly flat |
| Foam and filler | Cartridge | Joint length | Yes |
| Fabrication labour, then installation labour | Square metre, but charged as two separate rates | Factory time and site time, which are not the same trade | Dilutes in the factory, often not on site |
Now read that table as a warning. When a supplier flattens eight lines measured in five units into one rate per square metre, the flattening is a service to you — but it also hides every one of the eight decisions. Two quotations at the same rate per square metre can contain completely different consumptions, and neither is lying.
Chinese cost engineering has a fixed phrase for the big three: profile, glass and hardware. A widely reproduced cost-element breakdown puts profile at roughly thirty to forty percent of a window unit price, glass at roughly fifteen to twenty percent, and hardware at roughly eight to ten percent. Those shares are a source's arithmetic on a Chinese project, not a universal law and not ours — but the shape of the next part is what matters.
| Major material | How its supply price is formed | Consequence for the buyer |
|---|---|---|
| Aluminium profile | Ingot price plus a conversion fee plus long-distance freight | One of three terms is a traded commodity; the other two are work |
| Glass | Base glass price plus a processing fee plus long-distance freight | Exactly the same three-term shape, with a different commodity in front |
| Hardware | Per set, against a catalogue number and a brand | No commodity term at all. It changes when the load class changes, and not otherwise. |
Two of the three biggest lines in your window are built from the same three-part sentence: a commodity, some work, and some distance. That is why they are negotiable in the same way, and it is also why they are the two lines that carry a date. Hardware has no date in it, because hardware is a part number.
There is a second, quieter consequence. The conversion fee is quoted per tonne and moves with things that have nothing to do with your opening: the surface treatment ladder (anodising, powder, electrophoretic, fluorocarbon — a Chinese cost note describes fluorocarbon as roughly double powder), the anodising film thickness, and whether the section is thermally broken at all. A thermally broken section carries an added per-tonne charge for the polyamide strip, and an imported strip carries more. None of that is visible in a square-metre rate, and all of it is real.
This is the part of a wholesale price that almost no buyer reads, and it is the part that moves the most money on a long project. Because the profile price begins with an ingot price, and because the ingot price moves every day, the contract has to say which day. Published Chinese practice offers at least four candidates, and they can be weeks apart.
| Decision that must be written down | Options found in published practice | Why the choice is not neutral |
|---|---|---|
| Which day sets the ingot price | Bid issue date, bid return date, order date, or contract signing date | Each can be weeks apart. Whichever one the contract names is the one that governs. |
| Which publication is the reference | A domestic spot quotation for A00 primary aluminium; the Changjiang non-ferrous spot price is the most often named, with the Shanghai non-ferrous network and the China aluminium profile network also used | They are not the same series. A contract that names only "the market price" has named nothing. |
| How much movement is absorbed | One published bid document uses a band of plus or minus five percent; two cost references use plus or minus ten percent | We are not going to tell you which is right. The point is that there is no standard, so the band is a negotiation, not a fact. |
| What is excluded from adjustment | The conversion fee, the long-distance freight and the insulation strip are generally not adjusted; only the ingot term is | The commodity part of the price floats. The work part does not. Buyers routinely assume the whole line floats. |
| How a price is locked | A written lock-price notice, after which the average published over the following seven calendar days is treated as locked for that batch | If you never send the notice, you never lock anything, no matter what the contract says. |
| Whether glass floats too | In some bid documents, yes — against a local government market price publication, with its own band and a sharing factor applied to the excess | Two commodities, two triggers, two bands, two base dates. One clause rarely covers both. |
Read that table once more and the shape of the problem appears. A wholesale quotation for aluminium windows contains a date. If you did not choose it, it was chosen for you. And on a project where the interval between enquiry and final delivery is counted in months, the date is frequently worth more than the discount you negotiated.
There is a related mechanism that catches exporters and domestic buyers alike. A published Chinese procurement notice states plainly that the contract unit price equals the winning bid price while the settlement price floats. In other words, the number you negotiated is the number that gets signed; the number that gets paid is produced later, by a formula. Both statements are in the same document, and buyers who only read the first one are surprised at the end.
Now to something you can check yourself. Published Chinese cost sheets put the aluminium content of a thermally broken window at roughly nine to ten kilograms per square metre, and one of them converts that into a price exposure by stating the aluminium content explicitly. That coefficient is not a constant. It is a coefficient at a particular size.
Assume the profile section does not change, so that profile mass is proportional to total profile length, and approximate total profile length by the panel perimeter. Take a 1500 by 1500 millimetre window — the size used in the published worked example — with an area of 2.25 square metres and a perimeter of 6.0 metres. At ten kilograms per square metre that is 22.5 kilograms, or 3.75 kilograms per metre of perimeter. Now hold that section and change only the size.
| Panel, millimetres | Area, square metres | Perimeter, metres | Metres of perimeter per square metre | Implied kilograms of profile per square metre |
|---|---|---|---|---|
| 600 by 900 | 0.54 | 3.00 | 5.56 | 20.8 |
| 1200 by 1500 | 1.80 | 5.40 | 3.00 | 11.3 |
| 1500 by 1500 (published reference) | 2.25 | 6.00 | 2.67 | 10.0 |
| 2500 by 3000 (largest published single sash, SL126/182) | 7.50 | 11.00 | 1.47 | 5.5 |
| 2800 by 2600 (largest published single sash, SL155) | 7.28 | 10.80 | 1.48 | 5.6 |
This is our own arithmetic, built on a published consumption coefficient and two stated assumptions: unchanged section, and profile length approximated by perimeter. ｒｅｐｌａｃｅ either assumption and the numbers move. What does not move is the direction. Between a small window and the largest sash we publish, the aluminium carried per square metre falls by a factor of close to four — from roughly twenty-one kilograms per square metre to roughly five and a half. Glass, meanwhile, stays at about one square metre per square metre. The panel got bigger; the expensive line got cheaper per unit, and the line that stayed flat is not the expensive one.
We have written elsewhere that the cost of a window per unit area does not fall forever — that it is U-shaped, that very small units are pushed up by the fixed content of every sash and very large ones are pushed up again. The arithmetic above explains why the left-hand side falls. The right-hand side rises for a completely different reason, and the reason is that three of the consumption pools are not slopes at all. They are stairs.
| Pool | What forces a step | What we publish | What it does to the curve |
|---|---|---|---|
| Glass build-up | Span, weight, acoustic target and safety glazing rules | Two series publish cavity references, 24A and 27A, and the 27A unit is described as inert-gas filled. No series publishes glass thickness. | A heavier build-up re-prices the whole square metre and lowers the maximum panel. It also moves the date clause, because glass floats separately in some contracts. |
| Hardware | Sash weight, which is mostly glass weight | 200 kg load-bearing pulleys on TS130; up to 220 kg driving capacity on SL112/167; 400 kg on a twenty-wheel self-balancing carriage on SL155 | One step, not a slope. And note: driving capacity and load capacity are not the same measurement — do not sort them into one column. |
| Profile | Wind load and span | 1.8 to 2.0 mm on the window series; 2.0 mm locally reinforced to 3.0 mm on SL126/182; 1.8 to 2.5 mm on SL112/167; 2.2 to 2.5 mm on SL155 | Wall thickness is a conditional promise. It applies where the drawing says it applies, which is why a thinner number is not automatically a cheaper window. |
| Packing and handling | Size, weight and whether the unit still fits through a container door | Nothing. We publish no packing specification. | Changes the packing class, then the container plan, then the freight line — three steps that never appear in a per-square-metre rate. |
Put the two halves together and you get the real shape. Five pools dilute smoothly as the panel grows, and three of them stop diluting and jump. The curve looks like a U only because a slide and three staircases were drawn on the same axes. Once you see it that way, the useful question changes. Instead of asking whether a larger panel is cheaper, you ask at which of the three staircases your particular panel is standing.
Here is a consequence that very few buyers think about, and it follows directly from the table above. Profile is bought by weight and sold to you by area. Somebody has to absorb the gap, and the unit on your quotation tells you who.
If you are quoted a flat rate per square metre with no aluminium clause, the factory is carrying the weight risk: every kilogram it puts into the section comes out of its margin. That is a standing incentive to make the section lighter, and the incentive is invisible to you because you never see the weight. If instead your contract carries an aluminium adjustment clause keyed to a stated aluminium content, the commodity risk moves to you — and now the same incentive points the other way.
Published Chinese practice is unusually frank about how far this goes. Because profile is traded by the tonne, the weighing tolerance is a negotiated item — commonly agreed at a few parts per thousand. Because profile is wrapped before it is weighed, the wrapping is a negotiated item too: kraft paper packaging is capped at a stated number of kilograms per tonne, and switching to film packaging carries an added per-tonne charge. Packaging overall is put at a few percent of the total aluminium price. When you buy by the tonne, the wrapping paper is a contract line. That single fact tells you more about where the risk sits than any spreadsheet.
This is also why the phrase cheap swing door and the phrase "cheap thermally broken window" are both, strictly speaking, incomplete. A quotation that comes in far below the others is rarely the same window at a smaller margin. It is usually a different aluminium content, a different glass build-up, a different hardware set, or a different assumption about which day sets the ingot price — all four of which are invisible in a square-metre rate. Cheap is not a price. Cheap is a specification, and the specification is the part that was not written down.
A Chinese quotation-standard document for aluminium window and door works sets out what a proper quotation contains, and the list is longer than most buyers expect. Two items deserve quoting. First, the sheet must carry a quotation date and a validity period — typically thirty days from the quotation date, after which the price has to be re-established. Second, the quantity column should give both the unit count and the area, with the unit stated, because a rate per square metre without a unit count hides the fixed content of every sash.
| Element | Good form | What happens if it is missing |
|---|---|---|
| Quotation date and validity | A stated number of days from the date of issue | The rate is indefinitely revisable, and you find out at the wrong end of the project |
| Legal identity of the quoting entity | Full company name and stamp | You may be contracting with a name that is not the manufacturer |
| Schedule | Opening mark, opening type, width by height in millimetres, count, and area | Nobody can tell which unit a rate belongs to, and no two quotations are comparable |
| Profile line | Brand, series, theoretical weight, unit price per tonne or per metre, quantity, extension | The weight disappears, and with it the only link to the ingot clause |
| Glass line | Type, build-up, thickness, unit price per square metre, quantity | "Double glazed" is not a specification; it is a shape |
| Hardware line | Per set or per piece, with brand and model named | The load class is whatever is cheapest on the day |
| Gaskets, sealants and ancillaries | Material and specification named: fixings, foam, sealant, connectors, protective film | These are the first things quietly substituted, and the last things anyone inspects |
| Rate structure | If a composite rate is used, its composition is attached | You cannot tell which of the eight pools moved when the price changes |
| Applicable standard and quota version | Named, with version or edition | "Meets international standards" is not a document |
The same standard asks the quotation to state the scope of works explicitly: fabrication, transport, loading and unloading, installation, opening clean-out, perimeter filling, sealant, protection of finished surfaces, waste removal, attendance at handover, and service during the defects period. A separate cost-engineering commentary adds the interfaces that parties forget: who supplies and installs the sub-frame, who fills the joint between the main frame and the sub-frame and between the sub-frame and the wall, who makes good internally and externally, and who applies the internal and external sealant when the building is handed over shell-and-core rather than fitted out.
That commentary makes a point worth repeating in full, because it is the most accurate sentence in this whole subject: these items look small, and they can hold a programme up for days and turn into claims between parties that all believed someone else had them. The cheapest clause to write is the one that says who does the joint between the frame and the wall. The most expensive one is the clause that never mentions it.
| Document | What it fixes | What can still move | What usually surprises the buyer |
|---|---|---|---|
| Enquiry | Nothing | Everything | A vague enquiry does not produce a vague quotation. It produces a quotation full of assumptions. |
| Quotation | A rate, for a stated validity | Everything, until acceptance | The validity clock starts on the quotation date, not on the day you read it |
| Contract or proforma | The unit price and the adjustment mechanism | The settlement price, if a float clause exists | The signed number and the paid number are allowed to be different, and usually are |
| Final settlement | The amount, including any agreed adjustment | Only the retention | A published Chinese bid document releases payment to ninety-five percent of the settled amount once the second-round settlement report is internally approved, and holds five percent as quality guarantee money until the defects period ends. |
Two practical conclusions follow. If you want a fixed outcome, you need a fixed settlement clause, not a fixed unit price. And if you are comparing two suppliers, compare the settlement mechanism, not the rate — because the rate is the number both of them will change.
| Line | Why it is not in the square-metre rate | What to do about it |
|---|---|---|
| New section tooling | It is a one-off against a profile that does not exist yet | Ask whether it is charged, amortised against volume, or waived — and ask who owns the die |
| Samples and sample freight | A sample is a complete unit and is often packed better than production | Ask whether the sample cost is credited against the order, and in writing |
| Packing upgrade | Crate, corner protection, desiccant and stillage are a separate class of work | Specify packing on the order document, not in an email thread |
| Inland haulage, port charges and documentation | They sit outside the factory gate | Name the trade term and the named place. Both, not one. |
| Third-party inspection and testing | A test is performed on a specimen, and somebody has to book it | Say who pays, which standard with which version, and whether it is per batch or per order |
| Spare parts | Shipped later, they become a second shipment with its own freight bill and its own customs treatment | Put the critical spares into the original container. This is the single cheapest line in this table. |
There is a seventh line that belongs here because it is genuinely invisible. Published Chinese procurement documents sometimes state that where the buyer pays using a supply-chain finance instrument, the discounting cost falls to the supplier. That is worth reading twice: if your payment method pushes the cost of money onto the factory, that cost is already inside the unit price you were quoted. Payment terms are not a separate negotiation from price. They are the same negotiation, conducted in a different room.
We have written at length elsewhere about what wholesale actually changes: the unit of failure. Buy one window and an error is a fitting problem; buy two hundred and the same error is a logistics problem. What repetition genuinely does to price is narrower than most buyers assume. Published door-schedule guidance says it plainly — repetition lowers the unit price — but repetition means identical units. Two hundred doors spread over forty types produce forty first-offs, forty handing decisions, forty hardware sets and a packing list in which almost every line has a quantity of one.
There is a second, sharper version of the same point that comes from the aluminium side. Minimum quantities in this industry attach to a type and a finish, not to an order. A profile extrusion run and a powder-coating line both have a physical threshold below which they are not economic on their own — which is why a supplier who cheerfully accepts a very small order is often telling you, without saying it, that your goods will ride on somebody else's batch. That is not dishonest. It is the mechanism, and it is the same mechanism that produces colour drift between the eighth container and the first.
Everything we publish about a window is a performance number. Not one of the numbers on our product pages is a consumption number, and this is the honest reason we have no price list: the numbers that set the price are precisely the ones we do not print.
| We publish | What it actually measures | We do not publish | Why there is a gap |
|---|---|---|---|
| Thermal values of 1.3, 1.6 and 1.7 on three series | A system value for a stated configuration, not a whole-window value and not a value under another national scheme | A calculated value for your opening, your size and your glass build-up | That number belongs to a specimen that does not exist until you specify one |
| 240-hour salt spray and 5,000 newton shear strength | Coating and substrate corrosion on one series, and the composite bond between strip and aluminium on one series | Air, water and wind ratings for any series | Those two results are published test results for a named series. They do not transfer to other series, and they are not project qualifications. |
| 30,000 cycles on CMECH hardware | A bench result on a component, not a service life for a window | A cycle figure matched to your actual sash weight | Published Chinese specification practice asks for A-grade operating hardware to survive over 100,000 cycles and for rated capacity to exceed actual load by a stated factor. Our published figure is a different test on a different specimen. Ask which one your quotation is buying. |
| Load figures of 200, 220 and 400 kilograms | Per sash, and two of the three are different measurements entirely | The assumed glass build-up behind those figures | A maximum panel size is always published against an assumed glass thickness. Change the glass and the maximum changes. |
| Frame wall widths, sash thicknesses, sash widths, mullion widths, track heights | Dimensions of our own profiles — depth into the wall, sash stack, visible face, and the height of a water barrier | Aluminium content in kilograms per square metre, glass thickness, coating standard and film thickness | These are the consumption numbers, and they are exactly what a per-square-metre rate flattens away |
| Four standard colours plus custom matching | A stocked finish, versus a bespoke match with its own reference sample, tolerance and batch plan | Quotation validity, ingot base date and adjustment band, minimum per finish, packing specification | These are commercial terms, and they are answered per order rather than printed |
One more piece of honesty, because it belongs in a price article more than anywhere else. Our catalogue lists casement windows, a sliding window, tilt-and-turn windows and four sliding door series. The swing door, folding door, entry door, tilt-and-slide and sun-room category pages are empty. If your schedule calls for those, we will tell you so rather than quote a sliding door with a different name. Door operators, sensors and access control are a separate package again, normally sourced from specialist swing door opener suppliers rather than from a window and door factory, and they need three things that are not in any square-metre rate: a power position, a fixing path, and a service clearance.
The fastest way to a firm number is not to ask for a discount. It is to remove the assumptions. This block is designed to be pasted into an email; every blank you leave becomes a question later, and every question later costs more than the answer cost now.
| Send this | Why it changes the number | What happens if it is blank |
|---|---|---|
| A schedule with opening marks, width by height in millimetres, count, and how many units open | Hardware is bought per set and only for sashes that move | The supplier assumes a split, and you discover it at the factory drawing stage |
| Count of identical units per type, not the total count | Repetition lowers the unit price; variety does not | A large order is quoted as many small ones |
| Glass build-up: pane thickness, cavity, coating, gas fill, and any safety or acoustic requirement | It sets the weight, and the weight sets the hardware class and the maximum panel | "Double glazed" gets priced as the lightest build-up available |
| Series or profile depth required, and wall construction from outside to inside, layer by layer | Frame depth is a series attribute, not a function of track count | The frame arrives at a wall it was never measured against |
| Finish: a standard stock colour, or a custom match with a physical reference sample | A custom match is a specification with a tolerance, not a colour name | The nearest standard colour is substituted and nobody notices until installation |
| Hardware brand and model, or the performance it has to meet with a standard number | Hardware is the one major material with no commodity term | A grade word is substituted for a part number |
| Screens: yes or no, and which type | A screen is a second sash in the same opening, with its own cycle count | It becomes a second order, a second freight bill and a second colour batch |
| Threshold choice: low track, high track, or a high-ｄｒｏｐ track with a water barrier | It is a level decision, and levels are structure | It gets decided on site, after the floor is finished |
| Trade term with a named place, and who books the vessel | It decides where the factory's responsibility stops | Two quotations compared at the same rate are not comparable at all |
| Packing specification and whether spares travel in the same container | Packing is a class, and a second shipment has its own costs | The cheapest line in this table becomes the most expensive one in year three |
| Validity period you want, and the adjustment mechanism you will accept | The date inside the price is often worth more than the discount | The rate is real for thirty days and the project runs for nine months |
| Delivery sequence: which units arrive first, and in what order they are installed | Production order is the reverse of installation order, and someone has to plan it | The container arrives correctly made and in the wrong order |
| Ask this | A useful answer contains | Sounds reasonable, means nothing |
|---|---|---|
| What is the aluminium content of this unit? | Kilograms per square metre, or kilograms per unit, at your size | "We use a heavy-duty profile" |
| Which day sets the ingot price, and which publication? | A named event and a named price series | "Market price" |
| How far can it move before anything changes? | A stated band, and a stated list of what is excluded from adjustment | "We will be reasonable" |
| How do I lock it? | A written notice, a named recipient, and the averaging window that follows it | "It is locked" |
| Is the quoted rate the settled rate? | A clear statement of whether the settlement price floats | "The contract price is fixed" |
| What is the glass build-up, in millimetres, with coating and cavity? | Pane thickness, cavity, coating, gas, and the standard it is tested to | "Double glazed, Low-E" |
| Which hardware set, and what is it rated for? | Brand, model, rated capacity, and the standard and version it was tested to | "German hardware, heavy duty" |
| How long is this valid, and what happens on day thirty-one? | A number of days and a stated re-quotation process | "Valid for your project" |
| What is the minimum, and what does it attach to? | A quantity per type and per finish, not per order | "Small orders welcome" |
| What is packed, how, and what travels with it? | A packing specification and a spares list that ships in the same container | "Export standard packing" |
One last comparison point, because it is where per-square-metre rates break down most visibly. A fixed pane and an opening light in the same hole do not sit on one line. Asking for a single tilt and turn windows price to cover a mixed elevation produces an averaged number that fits no unit in it, and it makes the fixed panes subsidise the opening ones in a way nobody intended.
Because the two biggest cost lines in a window start with a commodity price and a consumption quantity, and neither is known until the specification is. A list would have to assume a size, a glass build-up, a hardware set, a finish and a quantity per type. Publish those assumptions and the list is a quotation with extra steps; leave them out and the list is a number nobody will honour.
It should, and mostly it does, because five of the consumption pools dilute as the panel grows — we showed aluminium content per square metre falling by close to four times between a small window and our largest published sash. What stops the fall is three staircases: a heavier glass build-up, a step up in hardware load class, and local reinforcement of the profile. Ask where your panel is standing on each of the three.
The one naming the day that sets the aluminium ingot price, together with the publication it is read from and the band inside which nothing changes. Buyers negotiate the rate for a week and sign the base-date clause in a minute. On a long project the clause is frequently worth more than the discount.
No, and published Chinese procurement documents say so explicitly: the contract unit price equals the winning price, while the settlement price floats according to the agreed mechanism. If you want a fixed outcome you need a fixed settlement clause, a lock-price notice procedure you actually operate, or a validity period that covers your decision window.
Ask for the four consumption numbers that a per-square-metre rate hides: aluminium content in kilograms per square metre, glass build-up in millimetres, the hardware set with its rated capacity, and the coating standard with film thickness. Then ask which day sets the ingot price. A supplier who answers all five is comparing like with like; one who answers none of them is not cheaper, just quieter.
The glass build-up. It sets the weight, the weight sets the hardware class, the hardware class sets part of the price, and the maximum panel size was published against an assumed build-up in the first place. Locking the glass locks four other decisions that would otherwise be made for you.
