How much paint do I need?
27 September 2026 · 4 min read · by Rodney Lee
The most common paint-buying mistake isn't picking the wrong colour — it's picking up the wrong number of tins. Buy too little and the merchant has run out of the batch by the time you're back; buy too much and a dozen unopened tins end up in the garage. Here's how to get it right the first time.
1. Measure the walls, not the floor
Wall area is the distance around the room (the perimeter) multiplied by the ceiling height. A 4 m × 4 m room has a 16 m perimeter; at a 2.4 m ceiling that's 38.4 m² of wall.
- Doors: knock off roughly 1.8 m² each.
- Windows: knock off roughly 2 m² each (a standard casement).
- Skirting, coving and picture rails are usually painted separately or with the same tin — a little spare is fine.
In our example: 38.4 − 1.8 − 2 ≈ 34.6 m² of wall to paint.
2. Multiply by coats
Most walls need two coats, and a big change of colour (white over dark red, say) often wants a third or a separate primer. Budget for two coats on anything except a like-for-like repaint.
3. Divide by coverage
Check the tin, but most UK emulsions cover around 10–12 m² per litre per coat. Cheap paint often covers less; good trade paint usually covers more. Using 10 m²/L for the example:
34.6 m² × 2 coats ÷ 10 m²/L ≈ 7 litres. That's three 2.5 L tins, or one 5 L plus a 2.5 L.
4. Add a little spare, not a lot
Add roughly 10% for spillage, roller losses and touch-ups. Seven litres becomes about 7.5–8 L. If the wall is fresh plaster, expect the first coat to soak in more — mist-coating new plaster uses noticeably more paint.
One last tip: keep the batch code from the tin. If you ever need to buy one more tin, matching the batch avoids a visible shade difference between walls.