How to measure a rectangular room
Measure the length and width of the room and the height of the walls. The wall area is 2 × (length + width) × height. Measure in metres, or convert feet to metres before calculating.
Subtract doors and windows
Subtract the space you will not paint. For quick estimates, our calculator uses 1.8 m² per door and 1.5 m² per window. Measure unusual openings separately for better accuracy.
Include coats and coverage
Multiply the paintable area by the number of coats, divide by the product coverage in m² per litre, then allow for touch-ups and waste. Fresh plaster may need a suitable primer or mist coat, so check the paint manufacturer’s instructions.
Example: a 4 m × 3 m room with 2.4 m walls
Wall area = 2 × (4 + 3) × 2.4 = 33.6 m². Subtract one standard door (1.8 m²) and two windows (3 m²) to get 28.8 m². With two coats at 12 m²/L, plus 10% allowance, that is about 5.3 litres.
Frequently asked questions
Does it include the ceiling?
The room calculation covers the walls by default. Tick “Include the ceiling” in the calculator if you also want that area in the same estimate.
What if the room is L-shaped?
Break irregular rooms into separate rectangular sections, work out each wall area, and add them together.
These calculations are estimates. Always follow the product’s coverage, preparation and application instructions.