Paint calculator for several rooms and walls
Start with the room width, depth and wall height. The calculator creates four starting walls and keeps their widths in step with the room dimensions. Edit any wall separately, add extra walls for alcoves or irregular spaces, and add another room for a whole-home estimate.
Paint calculation formula
Litres = net wall area × coats ÷ 12 × extra allowance. Net wall area is the wall width multiplied by height, minus any doors and windows you enter. The calculator uses 12 m² per litre as a sensible planning rate for standard interior emulsion, so it does not ask you for a technical product figure.
Paint type, surface porosity, application method and a major colour change can alter the real amount. Treat the result as a planning estimate and compare it with the instructions on the exact tin before buying.
How to measure walls for paint
- Measure the width and height of each wall.
- Multiply door or window width by height and add those openings together.
- Enter each wall separately, including short returns or alcoves.
- Choose the number of coats and leave a little extra for touch-ups.
Should I add 10% or 20% extra paint?
Ten percent is a practical default for normal application and future touch-ups. Increase it towards 15–20% for rough or porous walls, difficult access, a major colour change, or when you want a larger reserve. Extra coats usually have more effect than the waste percentage.
Plan the rest of the project
View all free project calculators →
Frequently asked questions
Can I calculate paint for several rooms?
Yes. Select “Add room”, then add or remove individual walls inside each room.
Does the calculator account for two coats?
Yes. Two coats is the default, and you can change it for one-coat products, primer or a third coat.
How do I account for doors and windows?
Enter their combined area for each wall. Leave the field at zero if you do not know it; the estimate will simply include the whole wall.