Estimate how much paint a room needs from its dimensions, doors, windows and number of coats.
How paint is worked out
This paint calculator works out the paintable wall area of a room, subtracts doors and windows, and estimates the paint needed for your number of coats — using a typical coverage of about 350 square feet per gallon.
Buy a little extra for touch-ups.
The default scenario, worked through
On the values this calculator opens with, the paint needed is 2.4. Underneath, Paintable area comes out at 417 ft² and Litres at 9 L. Change any field and every figure updates as you type.
How to use it
- Enter the room length, width and wall height.
- Enter the number of doors, windows and coats.
- Read the gallons (and litres) needed.
The calculation
wall area = 2 × (length + width) × height − doors − windows
gallons = area × coats ÷ 350
Questions people ask about this
How much does a gallon of paint cover?
About 350 square feet per coat on smooth walls, less on rough or porous surfaces.
Do I need two coats?
Often yes, especially over a different colour or bare surface. The calculator lets you choose.
Should I buy extra?
Yes — a little extra covers touch-ups and future repairs, and matching later batches can be tricky.