Paint Calculator
Estimate litres and cans of paint for a room’s walls (and ceiling), minus doors and windows.
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About the Paint Calculator
Enter the size of the room and the number of doors and windows to estimate the paint for its walls — and the ceiling, if you tick that option.
The default coverage is 10 m² per litre per coat, typical for emulsion on a smooth, primed wall, and the default can size is 3.64 litres (one gallon tin). Check the label of your paint and adjust these if needed.
How to use the Paint Calculator
- Choose feet or metres and enter the room length, width and wall height.
- Enter the number of doors and windows.
- Choose the number of coats and whether to include the ceiling.
- Adjust coverage and can size if needed, then click Calculate paint.
Formula
Wall area = 2 × (length + width) × height.
Openings: each door ≈ 1.9 m² (about 20 sq ft), each window ≈ 1.4 m² (about 15 sq ft).
Paintable area = wall area − openings (+ length × width for the ceiling).
Litres = paintable area × coats ÷ coverage per litre. Cans = litres ÷ can size, rounded up.
Examples
- A 12 × 10 ft room with 10 ft walls, 1 door, 2 windows, 2 coats: 389 sq ft (36.2 m²) to paint → 7.3 litres, about 2 cans of 3.64 L.
- Adding the ceiling (120 sq ft) increases it to 9.5 litres, about 3 cans.
Frequently asked questions
How accurate is this estimate?
It is a planning estimate based on standard formulas. Actual quantities depend on workmanship, material quality and site conditions, so confirm with your contractor or engineer before buying.
How many coats do I need?
Two coats are normal for a good finish. New plaster, a big colour change or dark colours may need a primer and a third coat.
Why is my wall using more paint than expected?
Rough, porous or unprimed walls absorb more paint. Lower the coverage per litre for these surfaces.