Wall Paint Calculator
Work out how much paint the walls of a room need — doors and windows deducted, coats counted, and your paint's own coverage used.
Walls are where most paint goes, and where most estimates go wrong — doors and windows are forgotten, or the coverage is guessed. This calculator deducts the openings and uses your paint's real coverage.
Measure the room, count the openings, and the calculator does the rest. For the ceiling, use the ceiling paint calculator.
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
- Measure the room length, width and height.
- Count the doors and windows — they are deducted automatically.
- Enter coats (usually 2) and the coverage from the tin.
- Add a price per gallon or litre if you want a cost estimate.
Worked example
| Room | 12 ft × 15 ft × 8 ft high |
|---|---|
| Gross wall area | 2 × (12 + 15) × 8 = 432 ft² |
| Deductions | 1 door (21 ft²) + 2 windows (2 × 15 ft²) = 51 ft² |
| Paintable area | 432 − 51 = 381 ft² |
| Paint (2 coats, 350 ft²/gal) | 381 × 2 ÷ 350 = 2.18 gallons |
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
Do I deduct doors and windows from wall paint?
Yes. A door is about 21 ft² (1.95 m²) and a window about 15 ft² (1.39 m²) that you will not paint. This calculator deducts them automatically — the figures are stated on the page.
How many coats for walls?
Two coats is the standard for walls, especially over a new colour or new plaster. One coat is enough only when repainting the same colour over sound paint.
What is the difference between this and the paint calculator?
This page works the wall area out from the room and deducts openings. The paint calculator takes an area you already know — use it for a single wall, a feature wall, or a figure from a quote.
Do I need primer on walls?
On new plaster, bare drywall or a big colour change, yes — primer seals the surface so the topcoat covers evenly. Use the primer calculator for the primer quantity.
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.