A paint calculator estimates the amount of paint needed to cover a wall or room based on the wall dimensions, the paint's coverage rate (how many square metres one litre covers) and the number of coats to be applied. It also adds a 10% waste factor to account for edges, touch-ups and uneven application.

1. Enter the average wall length and height.
2. Enter the number of walls to paint.
3. Enter the paint coverage rate (check the tin — typically 10–14 m²/litre).
4. Enter the number of coats.
5. Click Calculate.

Room: 4 walls, each 5m × 2.4m = 48 m²
Coverage: 10 m²/L, 2 coats
Paint needed: (48 × 2) ÷ 10 = 9.6 L + 10% waste = 10.56 L

The coverage rate on paint tins is a theoretical maximum on a smooth, primed surface. Rough or porous surfaces absorb more paint. Darker colours may require more coats. Always buy slightly more than the calculated amount — having leftover paint for touch-ups is valuable.

• Using the coverage rate for a single coat when planning multiple coats — multiply by the number of coats.
• Not accounting for doors and windows — subtract their area from the total wall area for a more accurate estimate.

What is a typical paint coverage rate?

Most interior wall paints cover 10–14 m² per litre on a smooth, primed surface. Check the specific product you are using — coverage varies by brand and paint type.

Should I subtract doors and windows?

For a rough estimate, it is often easier to ignore them and treat the extra paint as your waste buffer. For a more precise estimate, subtract the area of each door (approximately 2 m²) and window (approximately 1.5 m²).