Free online tool
Window & Door Size Converter
Quoting a window in millimetres to a customer who works in feet and inches? Convert the size, the unit area, the total area for a quantity and the order value at your price per square metre.
Quick reference — metric sizes and their imperial equivalent:
900 × 1200 mm = 35.4 × 47.2 in
1200 × 1500 mm = 47.2 × 59.1 in
1500 × 1500 mm = 59.1 × 59.1 in
1800 × 2000 mm = 70.9 × 78.7 in
Size and order value
Aluminium window and door sizes are custom-made to the millimetre, so tell us the opening size rather than the frame size and we will build to the structural opening. Our 55 / 80 / 90 / 93 / 108 series cover residential, hotel and commercial projects.
Jump straight to a system: 55 series · 80 series thickened · 90 series thickened · 93 series thickened · 95 series · 98 series · 108 series · FG110F broken bridge
Send the numbers to us
Send your size list and we will quote the whole window or door package.
How it works
How to convert window and door sizes
Three conversions cover almost every window and door calculation:
- Millimetres to inches = millimetres ÷ 25.4. The result is then split into feet and inches (1 ft = 12 in).
- Area of one piece = width × height, in millimetres, divided by 1,000,000 to get square metres.
- Total area = area of one piece × quantity. Square feet = square metres × 10.7639.
Add your price per square metre and the converter returns the estimated order value, which is the fastest way to sanity-check a quotation you received by email.
Common metric sizes and their imperial equivalents
| Metric (mm) | Inches | Feet and inches | Area |
|---|---|---|---|
| 600 × 1200 | 23.6" × 47.2" | 1' 11.6" × 3' 11.2" | 0.72 m² / 7.75 ft² |
| 900 × 2100 | 35.4" × 82.7" | 2' 11.4" × 6' 10.7" | 1.89 m² / 20.34 ft² |
| 1200 × 1200 | 47.2" × 47.2" | 3' 11.2" × 3' 11.2" | 1.44 m² / 15.50 ft² |
| 1500 × 1500 | 59.1" × 59.1" | 4' 11.1" × 4' 11.1" | 2.25 m² / 24.22 ft² |
| 1800 × 2400 | 70.9" × 94.5" | 5' 10.9" × 7' 10.5" | 4.32 m² / 46.52 ft² |
| 2100 × 2400 | 82.7" × 94.5" | 6' 10.7" × 7' 10.5" | 5.04 m² / 54.25 ft² |
Why window sizes differ between suppliers
- Opening size versus frame size. The structural opening in the wall is normally 10-20 mm bigger than the frame that fills it.
- Tolerance. Finished aluminium frames are produced with a tolerance of about +/- 1-2 mm, so the size on the quotation is never the size on the measuring tape.
- Series and profile depth. A 55 series, 80 series and 93 series window of the same opening size have different frame widths and therefore different glass areas.
- Glass area is not frame area. Heat load, U-value and daylight are calculated on the glass area, while the order value is based on the frame size.
- Custom versus stock sizes. Standard stock sizes are cheaper and faster; custom sizes are made to order and usually need a longer lead time.
- Local codes. Minimum and maximum sizes per series differ by market, so a size that is normal in Europe may fall outside the range in the Gulf or in North America.
What to send for an aluminium window quotation
- A size list: opening width and height in millimetres per position, with the quantity per size.
- Number of openings and a photo or drawing of each elevation.
- Glass specification: single, double, laminated, tinted or low-E, and the gas fill if double glazed.
- Frame finish: powder-coated colour, anodised, wood grain or a specific RAL reference.
- Opening type: fixed, casement, awning, sliding, tilt-and-turn, plus the handle and hardware preference.
- Installation detail: sill, waterproofing, and whether the opening is a new build or a replacement.
Frequently asked questions
How do I convert millimetres to inches?
Divide the millimetre value by 25.4. For example 1500 mm is 59.06 inches, which is 4 feet and 11.1 inches. The converter above does the division, splits the result into feet and inches and shows the area of the piece in both square metres and square feet.
What is 1500 x 1500 mm in feet and inches?
1500 mm is 59.1 inches and 1500 mm in height is also 59.1 inches, so a 1500 x 1500 mm window is 4 feet 11.1 inches by 4 feet 11.1 inches, with an area of 2.25 square metres or 24.22 square feet.
How do I convert square metres to square feet?
Multiply by 10.7639. A 2.25 square metre window is 24.22 square feet. The converter applies this automatically and also multiplies by the quantity, so a run of 40 windows of that size gives the total ordered area of 90 square metres.
How do I measure a window for replacement?
Measure the opening width at the top, the middle and the bottom, and the height on the left, the middle and the right, then use the smallest figures. Measure in millimetres to one decimal place and note whether the frame is still in place, because the opening size and the frame size differ.
Where this calculator leads
Get aluminium windows and doors quoted
We manufacture aluminium windows and doors in 55, 80, 90, 93 and 108 series with thermal break, in custom sizes, exporting to 50+ countries. Send the converted sizes and quantities and we quote the profile, glass and hardware options with loading quantity and shipping.