Standard window sizes in the UK, and why your opening rarely matches
There is no official UK standard window size. What the trade calls "standard sizes" are conventions inherited from imperial brickwork: widths like 488mm, 630mm, 915mm, 1200mm and 1770mm that fitted whole numbers of bricks in mid-century housing. If your house matches one, a stock window might fit. Most don't: settlement, render, rebuilt reveals and metric-era construction mean real openings land anywhere.
That's why we don't sell stock sizes at all. Every window is made to your measurement, from 300mm to 3000mm wide and 430mm to 3030mm high overall (cill included), depending on the style, at a price computed from the actual materials. A made-to-measure 887×1043mm window doesn't cost more than a hypothetical "standard" one. We supply only: you measure and order, we make and deliver, and you or your fitter install.
The traditional size grid
Old joinery catalogues worked to a grid of widths and heights, and you'll still see merchant stock windows sold on it:
| Item | Sizes (mm) |
|---|---|
| Traditional widths | 488 · 630 · 915 · 1200 · 1770 · 2340 |
| Traditional heights | 450 · 600 · 750 · 900 · 1050 · 1200 · 1350 · 1500 |
| Made to measure (ours) | Any width from 300 to 3000, any height from 430 to 3030 |
It's worth knowing only so you can check how far your opening deviates: measure yours and it will usually be 10-60mm off the nearest grid size, which is exactly the gap that causes bodged packing and wavy silicone lines on stock-window installs.
What actually matters: your opening
- Measure the brick-to-brick opening width and height in three places each; use the smallest
- Deduct 10mm from each dimension for fitting clearance. That's the overall size to order, including the cill if you choose one
- Our windows go from 300mm to 3000mm wide and 430mm to 3030mm high overall, covering everything from a WC vent light to a full-width lounge window. Each style's page gives its own range
- Inside the frame, a side-hung sash can be 400-900mm wide and up to 1300mm tall, a top-hung vent 400-1300mm wide with a 400-1300mm drop, and pane sizes are governed by the glass-sheet limits the designer enforces
Sizes and cost
Price scales with the frame metres and glass area your sizes generate, plus the options you choose, not with whether the numbers are round. Two windows a few millimetres apart price a few pence apart. The only steps you'll notice are physical ones: a second opener adds hardware, and very large panes move into different glass handling.
Frequently asked questions
- What are standard uPVC window sizes in the UK?
- Conventionally: widths around 488, 630, 915, 1200 and 1770mm against heights from 450 to 1500mm: imperial-brickwork leftovers, not a regulation. Made-to-measure removes the question.
- What's the biggest window you can make?
- Up to 3000mm wide and up to 3030mm high overall, depending on the layout; each style's page gives its own range. Individual panes must stay within glass-sheet limits (up to 1299mm in one direction and 2300mm in the other), which the designer enforces automatically with mullions and transoms.
- What's the smallest?
- 300 × 430mm overall, cill included: our Picture Window (Fixed), small enough for cloakroom and utility windows. The smallest window that opens is a Full Top-Hung Window at 500 × 430mm.
- My opening is bigger than 3000mm wide. What do I do?
- Wide openings are built from coupled frames. Order the sections as separate windows and join them on site with a coupler. Our frame-extender options include a 10mm coupler priced per metre.
- Should I order the opening size or the frame size?
- Order the overall size: your brick-to-brick opening minus 10mm in each direction. It includes the cill if you choose one. The measuring guide shows the whole process with diagrams.
Ready to price your sizes?
Pick a style, type your measurements and watch the price update as you choose colours, glass and hardware.