If you have ever tried to order a sliding window from a metric catalogue using an imperial size chart, you already know the problem: the numbers are close, but they are never equal. A 60 x 48 sliding window is not a 1500 x 1200 window, and the 24 mm of daylight between those two figures is exactly where installation trouble starts. This guide is about reading metric sliding window sizes properly — what the published ranges actually are, where they come from, and which single millimetre value belongs on your purchase order.
The word "standard" implies an authority behind it. For window sizes there is no such authority in most markets. What exists instead is a set of catalogue conventions — ranges that individual fabricators chose because they suit the way their own extrusion lengths, glass stock and roller templates are cut. Two suppliers in the same country can publish different "standard" ranges and both be correct.
The unit system is a separate problem layered on top. North America sizes windows in feet and inches and often refers to them by a four-digit code, where the first two digits are width and the last two are height: a 4030 is 4 ft 0 in wide by 3 ft 0 in tall, or 48 x 36 inches. Almost everywhere else designs in millimetres. Neither system is wrong, but they do not round into each other, and that is the part that catches people out.
An inch is 25.4 mm exactly, so converting is arithmetic, not estimation. The trouble is that a converted imperial size lands on an awkward millimetre number, while metric catalogues are built on round modules — usually 100 mm or 300 mm steps. Someone has to give, and the person who gives is usually the person cutting the wall.
| Imperial callout | Inches W x H | Exact millimetres | Nearest round metric module | Difference W / H |
|---|---|---|---|---|
| 2020 | 24 x 24 | 610 x 610 | 600 x 600 | 10 / 10 mm |
| 3020 | 36 x 24 | 914 x 610 | 900 x 600 | 14 / 10 mm |
| 4030 | 48 x 36 | 1219 x 914 | 1200 x 900 | 19 / 14 mm |
| 5030 | 60 x 36 | 1524 x 914 | 1500 x 900 | 24 / 14 mm |
| 5040 | 60 x 48 | 1524 x 1219 | 1500 x 1200 | 24 / 19 mm |
| 6040 | 72 x 48 | 1829 x 1219 | 1800 x 1200 | 29 / 19 mm |
| 6050 | 72 x 60 | 1829 x 1524 | 1800 x 1500 | 29 / 24 mm |
None of these differences are large enough to matter to a drawing, and every one of them is large enough to matter to a rough opening. If your framing was cut for a 1524 mm unit and you order a 1500 mm unit, you are packing 24 mm of shim and sealant into a gap that was designed for about half that. The rule that avoids the whole mess: convert once, early, then design in millimetres and never convert back.
Most sizing disputes are not about millimetres at all. They are about two people using the same word for four different measurements.
| Term | What it measures | Who uses it |
|---|---|---|
| Nominal callout | The label, e.g. 5040 or "1500 x 1200". A shorthand, not a measurement | Catalogues, take-offs |
| Actual frame size | Outer edge of the aluminium frame to outer edge | The factory — this is what you order |
| Rough opening | The hole in the wall. Always larger than the frame, to allow shims, levelling and sealant | Framing carpenter |
| Clear opening | The gap left once the sash is fully open. On a two-panel slider this is roughly half the frame width, minus the sash stiles | Ventilation and egress checks |
Put the actual frame size in millimetres on the purchase order and let everyone else derive their own number from it. On the clearance question, installation guides in the trade commonly work to roughly half an inch of total shimming gap — about 12 to 15 mm — but that figure belongs to your supplier's installation detail, not to a general rule, so confirm it in writing before the wall is closed.
Because there is no single standard, the honest way to answer "what are the standard sizes" is to show what different fabricators publish. Below are three independently published sliding window ranges. Read them as evidence of how wide the convention is, not as a table to order from.
| Published by | Configuration | Width range | Height range |
|---|---|---|---|
| An Australian fabricator | Full sliding range, ~100 mm increments | 600 to 2100 mm | 610 to 2650 mm |
| A Chinese fabricator | Two-track | 600 to 1200 mm | 1200 to 1800 mm |
| Same Chinese fabricator | Three-track | 1200 to 2400 mm | 1500 to 2200 mm |
| A Chinese exporter | Single sliding | 600 to 1800 mm | 600 to 1500 mm |
| Same exporter | Double sliding | 1200 to 2400 mm | 600 to 1500 mm |
The overlap between these four sets is the useful answer. A practical metric band for residential sliding windows is roughly 600 to 2400 mm wide and 600 to 1800 mm tall, with taller units up to about 2400 mm appearing on the large end. Anything beyond that is not a size lookup any more; it is an engineering conversation about sash weight, glass build-up and roller capacity.
A casement window is constrained by how far a sash can swing. A sliding window has no such limit, so width becomes the free variable — and the frame depth becomes the bill you pay for it. Every extra track needs its own channel in the extrusion, so the frame gets deeper as the configuration grows.
Here is how that plays out across the ALPES sliding range. Note that the frame wall width is the number that has to physically fit inside your wall reveal:
| Series | Frame wall width | Sash width | Glass sash thickness | Track height |
|---|---|---|---|---|
| TS130 side press | 130 mm | 75 mm | 55 mm | 53 / 31 mm |
| SL112 / 167 | 112 mm (1–2 track) / 167 mm (3 track) | 53 or 75 mm | 43 mm | 45 mm high-ｄｒｏｐ bottom track, optional 85 mm barrier |
| SL126 / 182 (96) | 126 mm (2 track) / 182 mm (3 track) | 96 mm | 55 mm | 43 mm high / 8 mm low |
| SL126 / 182 (75) | 126 mm (2 track) / 182 mm (3 track) | 75 mm | 55 mm | 43 mm high / 8 mm low |
| SL155 four-track | 155 mm | 44.5 mm | 54.5 mm | Not published — request the cross-section |
One honest observation from that table: frame depth does not rise neatly with track count across different series. The four-track SL155 is 155 mm deep, which is deeper than the 126 mm two-track SL126 but shallower than the 182 mm three-track SL126. Depth is a property of the series, not of the number of tracks. If wall depth is tight, compare the actual frame wall width rather than assuming "more tracks means deeper".
A sliding sash does not hang off a hinge, it rides on rollers. That single fact sets a ceiling on size that has nothing to do with the wall opening: at some point the sash is simply too heavy to move nicely. Published load figures are the nearest thing to an honest "maximum size" you will find.
Glass is where most of that weight comes from. The 27A insulated unit with inert gas filling on the SL126/182(75) is a very different load from a slim 24A unit, and it changes the roller specification, not just the price. When you ask for a large unit, ask for the sash weight along with the dimensions.
One thing to be straight about: ALPES publishes K-values for its casement and tilt-turn series — 1.3 for the AW90 passive window, 1.6 for the C120 and 1.7 for the C116 — but no thermal figure is published for the sliding series. That is not an oversight in this article; it is how the catalogue reads. If thermal performance is the driving requirement, ask for a whole-window U-value and SHGC calculated on the exact glass build-up you intend to order, and compare it against the published casement numbers rather than assuming the sliding unit matches them.
Sliding windows are naturally wide and short. Every published range above reflects that: heights cluster between 600 and 1500 mm, with the tallest standard units reaching roughly 1800 to 2400 mm. Past that point three problems arrive together — the sash gets heavier, the roller has to work harder against a taller lever arm, and the handle ends up somewhere a person of average height cannot comfortably reach while the sash is at the far end of its travel.
If you need a tall opening, the usual answer is a transom: a fixed panel above or below the sliding section, so the moving sash stays in a comfortable size band while the overall unit gets taller. Note that a transom changes the clear opening calculation, so re-run it after you add one.
Frame wall width on the ALPES sliding range runs from 112 mm to 182 mm. In a new build you design the wall around the window. In a renovation you inherit a wall, and if the reveal is 100 mm, the deeper three-track and four-track series are out before you look at a single width figure.
Measure the reveal depth at the same time you measure width and height, and write it on the order sheet. It is the measurement most often missing from enquiries, and it is the one that cannot be fixed with a shim.
Standard metric modules exist because they save money on both sides of the order: stock lengths cut with less waste, rollers and locks matched to factory templates, and installers who already know how the unit sits in a conventional opening. That advantage is real, and it is the reason to design around a catalogue range whenever the design allows it.
| Situation | Better choice | Reason |
|---|---|---|
| Opening lands within about 10 mm of a catalogue size | Standard module plus packing | The gap is within what shims and reveals are designed to absorb |
| Difference exceeds about 20 mm, or the height is non-standard | Custom size | Heavy packing compresses the weather seal and leaves visible gaps |
| Replacement into an existing frame | Measure the old frame and order to that | The wall is already built; the frame is the only number you control |
| Long run of identical openings | Custom is often worth quoting | One-off setup is spread across the whole quantity |
| Opening over roughly 2400 mm in either direction | Engineering review, not a size lookup | Sash weight, glass build-up and roller rating now drive the design |
Custom sizing carries a premium and extra lead time, and no honest supplier will pretend otherwise. Set that against the cost of site remedial work, which is almost always higher and almost never budgeted. Get both numbers before you decide.
Most delayed quotes are delayed because an enquiry said "about 1500 wide" and the factory had to ask six questions. Send these ten lines and you will usually get a price back on the first pass.
| Line | What to write | Why it matters |
|---|---|---|
| 1 | Actual frame width x height in millimetres, stated as frame size | Removes the nominal-versus-actual argument entirely |
| 2 | Reveal or wall depth in millimetres | Decides which series physically fits |
| 3 | Track count and which panels move | Sets frame depth and the clear opening fraction |
| 4 | Glass build-up, e.g. 24A or 27A with gas filling | Drives sash weight, and therefore the roller rating |
| 5 | Sill height and any transom position | Changes reach, safety and the clear opening |
| 6 | Threshold preference: low track or high track | 8 mm low track for level access, 43 mm high track for weather exposure |
| 7 | Mesh specification and which side it sits on | Affects the sash stack-up and the interior sightline |
| 8 | Named hardware brand | ROTO, Winkhaus, CMECH and Wehag are all available — name one so the quote is comparable |
| 9 | Quantity per distinct size | Determines whether custom tooling is worth setting up |
| 10 | A dimensioned drawing or marked-up elevation, in millimetres | One drawing answers questions that ten emails cannot |
At the bottom of the range the constraint flips. A small sliding window around 600 x 600 mm has no weight problem at all, but it has a proportion problem: the interlocking stiles and the roller housing take a fixed amount of width out of the opening regardless of how small the unit is, so the clear opening shrinks as a percentage much faster than the frame does. Below roughly 600 mm in width, a casement or an awning sash usually gives you more usable ventilation for the same hole in the wall, and it will seal better too.
Small sliders earn their place where a sash must not project — over a kitchen bench, into a corridor, or anywhere an outward-opening sash would foul a walkway. That is a real reason to specify one, and it is the only reason worth paying for.
No single one exists in most markets. What you find instead are overlapping catalogue conventions set by individual fabricators, which is why published ranges differ so much between suppliers. The practical residential band across the ranges published by several suppliers is roughly 600 to 2400 mm wide and 600 to 1800 mm tall.
Exactly 1524 x 1219 mm, because an inch is 25.4 mm. The nearest round metric module is 1500 x 1200 mm. Both numbers are correct for what they are, but only one of them should be on your order, and the rough opening must be cut for that same one.
1219 x 914 mm exactly, with 1200 x 900 mm as the nearest round module. That is a difference of 19 mm in width and 14 mm in height — small on a drawing, significant when the frame is already in the wall. If you are working from an imperial schedule, convert the whole schedule at the start of the project rather than unit by unit.
Trade installation guides commonly work to about half an inch of total clearance, roughly 12 to 15 mm, to allow for shims, levelling and sealant. Treat that as a starting point only: the binding figure is the one in your supplier's installation detail, so ask for it in writing before the opening is framed.
Within the ALPES sliding and sliding-door range, the published maxima are 2800 x 2600 mm per sash on the SL155 with a 400 kg pulley rating, and 2.5 m wide by 3.0 m tall on the SL126/182(96). These are engineering ceilings tied to a specific roller and glass specification, not catalogue sizes you can simply pick, and they must be checked against your wind load and glass build-up.
Give the factory both, but put millimetres on the purchase order. A millimetre drawing removes ambiguity at the machine, and it is the unit the extrusion lengths, glass cut sizes and roller templates are actually produced in.
There is no universal metric standard for sliding windows, only overlapping catalogue conventions that cluster around 600 to 2400 mm in width and 600 to 1800 mm in height. Convert imperial sizes once, early, and then design and order in millimetres. Put the actual frame size on the purchase order, measure the wall depth before you choose a series, and remember that the real ceiling on size is sash weight against roller capacity rather than anything printed in a size chart. Send the ten lines above with your enquiry and the quote will come back faster and argue with you less.
