Paint calculator: how many litres for your room
Free tool
Enter your room size, doors, windows and coats. You get the litres of paint and primer to buy, and the cans to ask for, in seconds.
Room details
How the paint calculator works
It finds the wall area, subtracts doors and windows, adds the ceiling if you want it painted, then divides by how far a litre of paint spreads on your wall type. It then multiplies by your coats and adds 10% for wastage and touch-ups.
Formula: litres = (wall area + ceiling area) × coats ÷ coverage per litre × 1.10. Wall area = 2 × (length + width) × height, minus 21 sq ft per door and 15 sq ft per window.
Typical coverage per litre
| Wall type | Sq ft per litre, per coat |
|---|---|
| Smooth, putty-finished | about 120 |
| Normal plastered wall | about 100 |
| Rough or textured | about 80 |
Always check the spread rate printed on your paint tin. Dark colours, new plaster and uneven walls drink more paint.
Questions, answered
How much paint do I need for a 12 × 10 ft room?
For a 12 × 10 ft room with 10 ft walls, one door and two windows, two coats of emulsion on the walls and ceiling take about 11 litres at 100 sq ft per litre, including 10% wastage, so plan on 12 litres. Use the calculator above to match your exact room.
How many coats of paint should I apply?
Two coats are the usual finish over primer. Use three coats when you are covering a dark colour with a light one.
Should I buy extra paint?
Yes. The calculator adds 10% for wastage. Keep a little spare for touch-ups, and buy all tins from the same batch so the shade matches.
Do I need primer?
On new plaster or putty, yes. Primer seals the wall, helps the colour look even and saves topcoat paint. The calculator adds one coat of primer if you tick the box.
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