Paint coverage calculator

Formula

How it works

Paint needed = area × coats ÷ coverage of the paint per litre, plus an allowance. The coverage is printed on the tin and varies with the product and the surface.

Worked example

The same calculation with the default values:

• Surface area to paint 40 m²
• Number of coats 2
• Coverage of the paint (per litre) 10 m²/L
• Waste allowance 10 %

1. paintable area = 40 × 2 = 80 m²
2. litres = 80 ÷ 10 × (1 + 10 ÷ 100) = 8.8 L
3. 8.8 L ÷ 3.78541 = 2.324714 gal (US)

Result: Paint needed (litres): 8.8 L · Paint needed (US gallons): 2.32471406 gal (US)

Common mistakes

• Forgetting to subtract doors and windows from the wall area before calculating - this calculator's area input should already exclude openings, or the result will overstate how much paint is needed.
• Using the coverage rate from a different paint type or finish than the one actually being bought - coverage per litre varies significantly between primer, matte, and gloss finishes, and between brands.
• Forgetting that a second (or third) coat rarely needs the exact same amount as the first - porous or dark-to-light repaints often need extra coverage on the first coat specifically, which a flat "coats × area" multiplication doesn't capture.