TidyToolsHow much paint do I need?
The amount of paint you need comes down to three things: the wall area, how many coats you're applying, and how far the paint stretches (its coverage). This calculator works out the wall area from your room's length, width, and height, subtracts a bit for doors and windows, multiplies by the number of coats, then divides by the coverage printed on the tin.
Wall area is roughly 2 × (length + width) × height — the perimeter of the room times how tall the walls are. From that we subtract a standard allowance for each door and window so you don't buy paint for surfaces you won't cover. Two coats is normal for a good, even finish; use one coat for a light refresh or three when going from a dark colour to a light one.
A worked example
A 4 m × 3 m room with 2.4 m walls has about 33.6 m² of wall. Subtract one door and one window and you're painting roughly 30 m². Over 2 coats that's 60 m² of coverage; at 10 m² per litre you need about 6 litres of paint — so a 5-litre tin plus a 1-litre, or round up to two 5-litre tins if you want spare for touch-ups.
Tips
- Check the tin's coverage — it varies by paint type (matt vs silk) and surface. Update the coverage field to match yours.
- Buy a little extra for touch-ups and to avoid running out mid-wall.
- Primer may be needed on bare or patchy walls — that's a separate coat.
- Textured or porous walls soak up more paint, reducing coverage.
Frequently asked questions
How do I calculate wall area for painting?
Multiply the room perimeter — 2 × (length + width) — by the wall height, then subtract the area of doors and windows. This calculator does it for you.
How many coats of paint do I need?
Two coats is standard for an even finish. Use one for a refresh in the same colour, or three when covering a much darker colour.
What coverage should I use?
Check the tin — typical emulsion covers about 10–13 m² per litre (roughly 350–400 sq ft per gallon), but textured or porous surfaces cover less. Enter your paint's figure for accuracy.