Paint Calculator
Work out how much paint you need for a room in litres, with doors and windows taken off and the right mix of 5L and 2.5L tins.
Reviewed by Dany, RightSums team · Updated
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home-energy · Daily life · UK & US
Enter the room size and the calculator works out the wall area, takes off doors (1.6 m² each) and windows (1.5 m² each), multiplies by the number of coats and divides by a realistic coverage figure for your walls. It adds 10% for roller loss and touch-ups, then suggests the fewest tins to buy. Paint tins quote a best case of up to 13 to 14 m² per litre; the calculator uses 12 m² for smooth painted walls and less for new plaster or rough surfaces.
Accepted inputs
- Room length and width
- Ceiling height
- Doors and windows
- Number of coats
- Wall surface
- Ceiling on or off
Outputs
- Litres of paint
- Wall area in m²
- 5L and 2.5L tin mix
How to use the Paint Calculator
- Enter the length and width of the room and the ceiling height. Most UK rooms are about 2.4 metres high.
- Add the number of doors and windows so their area is taken off the walls.
- Pick your wall surface. New plaster and textured walls soak up more paint than walls that are already painted.
- Read off the litres needed and the tins to buy. The figure already includes 10% extra for roller loss and touch-ups.
Frequently asked questions
How much paint do I need for a room?
Multiply the distance around the room by the ceiling height, take off about 1.6 m² for each door and 1.5 m² for each window, then double it for two coats and divide by 12. A 4 m by 3 m room with 2.4 m ceilings, one door and one window has 30.5 m² of wall, so two coats need about 5.6 litres with 10% spare: one 5 litre tin and one 2.5 litre tin.
How much does 1 litre of emulsion cover?
Dulux lists its standard Matt and Silk emulsions at up to 14 m² per litre and Easycare Washable Matt at up to 13 m². Those are best-case figures on smooth, sealed walls. Plan on about 12 m² per litre for a repaint, 10 m² for a big colour change and 7 to 8 m² on new plaster or rough walls.
How many coats of paint does a wall need?
Two coats is the norm for walls that are already painted. Going from a dark colour to a light one can need a third. New plaster needs a mist coat of watered-down emulsion first so the top coats stick and dry evenly.
How much paint do I need for a ceiling?
A ceiling is the room's length times its width. A 4 m by 3 m ceiling is 12 m², so two coats at 12 m² per litre need 2 litres, or 2.2 litres with some spare. One 2.5 litre tin is enough.
Should I buy extra paint?
The calculator already adds 10%, which covers what stays in the tray and on the roller plus a few touch-ups. Buy all the tins for one room at the same time, as colours mixed in store can vary slightly between batches.
Paint needed by room size
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