Window Area Calculator
Work out the total area of your windows — and how much of it is glass — from the count, the size and the frame percentage.
Window area is the whole unit; glass area is what is left after the frame. This calculator gives you both, from the count and the size.
Enter the windows; the areas follow.
Your results
Enter your measurements and press Calculate.
Quantities are rounded up to whole tiles, planks, boxes or bags, after the wastage allowance. Cost appears only when you enter a price.
Formula
All lengths are converted to a single unit before the calculation: 1 ft = 0.3048 m, 1 in = 25.4 mm, 1 ft² = 0.09290304 m², 1 yd² = 9 ft². Material quantities are rounded up — you cannot buy part of a tile, plank or bag.
How to use this calculator
- Enter the number of windows and their size.
- Enter the frame percentage.
- Read the area per window, the total area and the glass area.
Worked example
| Windows | 6 windows, 1.2 m × 1.5 m each |
|---|---|
| Area per window | 1.2 × 1.5 = 1.8 m² |
| Total area | 1.8 × 6 = 10.8 m² |
| Glass area (15% frame) | 10.8 × 0.85 = 9.18 m² |
Check it by hand: every step above uses the formula in the box. If your numbers match the example inputs but the calculator gives a different answer, please report it via the contact page.
Frequently asked questions
What is the glass area?
The total window area minus the frame — the part that lets light in. A 15% frame leaves 85% glass. Enter your own frame percentage if you know it.
Why does window area matter?
For glazing cost, heat loss, light levels and building regulations (which often ask for a minimum window area per room). This calculator gives you the total and the glass.
How do I measure a window's area?
Width × height of the whole window unit, frame included. The frame percentage then splits it into frame and glass.
Is this a substitute for building design?
No. This is an area calculation for planning. Structural requirements and building-code compliance vary by location — see the safety notice.
Related calculators
Estimates only. Results are for planning. Measure twice, confirm box coverage and tile sizes on the packaging you buy, and follow the manufacturer's instructions. See the disclaimer.