Paint calculator
Gallons or litres of paint for walls and ceilings
Type the room size, then the doors and windows to leave out. The example is a 12 x 14 ft room with 8 ft walls, one door, two windows and two coats.
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- Area painted
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- Cans or tins
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- Same amount, other units
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- Per coat
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An estimate of quantity from the sizes you typed, not an order list or a price. Check the coverage on your own tin, which varies by product, colour and surface.
How the amount is worked out
- Wall area = (length + width) x 2 x wall height, minus the doors and windows.
- Ceiling, if ticked, adds length x width.
- Paint = area x coats / coverage, plus the extra allowance.
Coverage is how much area one gallon or one litre covers in one coat. It is printed on the tin and varies a lot: rough, porous or new plaster soaks up more, and dark-to-light changes need more coats. Type your tin's figure for the best answer.
Worked example
Room 12 x 14 ft, walls 8 ft: (12 + 14) x 2 x 8 = 416 sq ft. Take off one door (20 sq ft) and two windows (2 x 15 = 30 sq ft): 366 sq ft. Two coats is 732 sq ft. At 350 sq ft per gallon that is 2.09 gallons; add 10% and it is 2.30 gallons, so 3 one-gallon cans.
Metric
Switch to metric to type metres and see litres. The coverage box converts the figure, but UK and Australian tins usually print their own (often 10 to 16 m² per litre), so type that instead.
What it does not cover
Primer, trim, doors and skirting are not included. Each can needs its own figure from its own tin. The calculator does not choose a product or say how a surface should be prepared.
Defaults and where they come from
Every default is only a starting point. Change any box to match what you are buying or building.
| Default | Value | Source |
|---|---|---|
| Coverage | 350 sq ft per US gallon (8.6 m² per litre after conversion) | Coverage printed on US interior wall paints is commonly 350 to 400 sq ft per gallon per coat; UK and Australian tins often print 10 to 16 m² per litre. Use your own tin's figure. |
| Door and window | Door 20 sq ft (36 x 80 in); window 15 sq ft (3 x 5 ft). Metric 1.9 m² and 1.4 m² after conversion. | A common US interior door is 36 x 80 in. Measure your own and change the boxes. |
| Extra allowance | 10% (usual 5 to 15%) | Common practice for rough surfaces, spills and touch-ups. No standard sets a figure. |
| Conversions | 1 US gallon = 3.785411784 litres | Exact (231 cubic inches). |