Work out how much paint to buy. This free paint quantity calculator turns room size or wall area and coats into gallons or litres, subtracting doors and windows and using adjustable coverage.
What to paint
ft
ft
ft
ft²
ft²
ft²/gal
Enter the room size (the calculator finds wall area) or a wall area directly. Default coverage is about 350 ft² per gallon (≈11 m² per litre) per coat — adjust to match your paint’s label.
Paint needed
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Enter your wall
Wall area
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With coats
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US gallons
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Litres
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Paint needed = wall area × coats ÷ coverage. Coverage varies by paint, surface and colour — porous or dark-to-light changes need more. Buy a little extra for touch-ups and uneven surfaces.
Use this free paint quantity calculator to work out how much paint you need. Enter your room size or wall area, the number of coats, and get the gallons or litres required.
What this paint calculator does
A paint quantity calculator turns your wall area and coats into the amount of paint to buy. Give it a room’s dimensions (it finds the wall area) or an area directly, in feet or metres.
How much paint you need
wall area = 2 × (length + width) × height − doors/windows
paint = wall area × coats ÷ coverage
A 12 × 10 ft room, 8 ft high has about 312 ft² of wall (minus openings) and needs roughly 1.8 gallons for two coats at 350 ft²/gallon.
Typical paint coverage
Measure
Coverage per coat
1 US gallon
~350 ft²
1 litre
~11 m²
5 litres
~55–60 m²
What changes how much you need
Number of coats, surface texture and colour change matter most. Porous, rough or previously unpainted surfaces soak up more, and big colour changes (dark to light) often need an extra coat. Buy a little extra for touch-ups.
How to use the paint calculator
Choose room size or wall area, and units.
Subtract doors and windows, set coats.
Read the gallons or litres required.
Paint Quantity FAQ
How much paint do I need?
Multiply wall area by the number of coats and divide by coverage. A 312 ft² wall at two coats and 350 ft²/gallon needs about 1.8 gallons.
How do I calculate wall area for a room?
Add the wall lengths and multiply by height: 2 × (length + width) × height, then subtract doors and windows.
How much does a gallon or litre of paint cover?
Roughly 350 ft² per US gallon, or about 11 m² per litre, per coat — though it varies by paint and surface.
How many coats should I use?
Usually two for an even finish. Big colour changes or porous surfaces may need a primer or an extra coat.
Should I buy extra paint?
Yes — round up and keep a little spare for touch-ups, and allow more for rough or unpainted surfaces that absorb more.
Is the paint quantity calculator free?
Yes, this paint quantity calculator is completely free, needs no sign-up, and gives instant results in your browser.
