Paint Calculator
Work out how much paint you need for a room — walls and, optionally, the ceiling — allowing for doors, windows and the number of coats, in US gallons or litres.
From the can — often 350–400.
Wall area = 2 × (length + width) × height, minus about 21 sq ft per door and 15 sq ft per window. Paint needed = area × coats ÷ coverage. Use the coverage printed on your paint; rough, porous or bare surfaces (new plaster, brick, wood) absorb more, and dark-to-light colour changes may need an extra coat or primer.
301
Paintable area (sq ft, one coat)
1.72
Paint needed (US gallons)
2
Buy (1-gallon cans)
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How to use paint calculator
- 1Choose US (feet, gallons) or metric (metres, litres).
- 2Enter the room's length, width and wall height, plus the number of doors and windows.
- 3Enter the number of coats and the coverage printed on your paint.
- 4Read the area, the paint needed and how many cans or tins to buy.
About this tool
Wall area is the room's perimeter × wall height: 2 × (length + width) × height. About 21 sq ft (1.95 m²) is subtracted for each standard door and 15 sq ft (1.39 m²) for each window. Paint needed = area × coats ÷ coverage. A 12 × 10 ft room with 8 ft walls, one door and two windows has about 301 sq ft of wall; two coats at 350 sq ft per gallon needs 1.7 gallons, so buy two.
Coverage varies by product, so the calculator uses the figure you enter — most interior emulsions and latex paints quote 350–400 sq ft per gallon or 10–12 m² per litre. Rough or porous surfaces (new plaster, bare wood, brick, textured walls) soak up more, and covering a dark colour with a light one may need a primer or an extra coat.
It's a planning estimate: buying slightly more than you need avoids colour differences between batches and leaves some for touch-ups. Doors, trim and skirting boards usually take a different finish and are worked out separately.
Frequently asked questions
With 8 ft ceilings, one door and one window, the walls are about 348 sq ft. Two coats at 350 sq ft per gallon need about 2 gallons.
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