How Much Paint Do I Need? A Room-by-Room Guide
Buying paint is easy to get wrong: too little means a second trip, too much means wasted money. This guide walks through measuring a room and turning it into litres and can sizes.
How Much Paint Do I Need? A Room-by-Room Guide
Buying paint is easy to get wrong: too little means a second trip, too much means wasted money. This guide walks through measuring a room and turning it into litres and can sizes.
The formula
Litres = total area × coats ÷ coverage rate × (1 + waste). Coverage is the area one litre covers in a single coat - typically 10 m² per litre for interior emulsion - and waste covers brushing losses and uneven surfaces, usually 10%.
Measuring the walls
Wall area is 2 × (length + width) × height. For a 4 m by 3 m room with 2.5 m ceilings that is 2 × 7 × 2.5 = 35 m². Measure each wall if the room is not rectangular.
Subtracting openings
Subtract doors and windows: a standard door is about 2 m² and a window about 1.5 m². Only deduct large openings - fiddling over small ones usually loses more accuracy than it gains.
Ceilings and coats
If you are painting the ceiling, add length × width. Two coats is normal; a big colour change or a porous surface may need three, so increase the coats value rather than guessing.
Buying the right cans
Round up to standard can sizes. A job needing 9.6 litres is best bought as a 10 L can plus a 1 L can for touch-ups, rather than five 2 L cans.
Frequently asked questions
What coverage rate should I use?
About 10 m2 per litre for typical interior emulsion. Check the tin, as coverage varies by product and finish.
Do I need to include the ceiling?
Only if you are painting it. Add length x width to the wall area.
How do I account for doors and windows?
Subtract about 2 m2 per door and 1.5 m2 per window from the wall area.
Is this suitable for a final purchase decision?
Use it for planning, then confirm against the tin coverage and your own measurements before buying.