Explanation
Paint coverage estimate
Paint quantity depends on the surface area, the number of coats and the product’s coverage. Entering the coverage yourself keeps the estimate tied to the paint you intend to use.
Measure the walls and read the label
Use net paintable area after subtracting doors and windows. Read the coverage rate from the product label (often 10 to 14 m² per litre), enter the coat count, then add any allowance explicitly.
P = A × n ÷ c × (1 + a/100)
| P | Paint to buy (L) |
|---|---|
| A | Wall area |
| n | Coats |
| c | Coverage |
| a | Allowance |
2 coats on 40 m²
| Wall area | 40 |
|---|---|
| Coats | 2 |
| Coverage | 10 |
| Allowance | 10 |
| Result | 8.8 L |
40 m² × 2 coats ÷ 10 m²/L = 8 L. Add the 10% allowance: 8 × (1 + 10/100) = 8.8 L.
1 coat on a 12 m² wall
| Wall area | 12 |
|---|---|
| Coats | 1 |
| Coverage | 6 |
| Allowance | 0 |
| Result | 2 L |
12 m² × 1 coats ÷ 6 m²/L = 2 L. Add the 0% allowance: 2 × (1 + 0/100) = 2 L.
3 coats on 30 m² with a 5% allowance
| Wall area | 30 |
|---|---|
| Coats | 3 |
| Coverage | 9 |
| Allowance | 5 |
| Result | 10.5 L |
30 m² × 3 coats ÷ 9 m²/L = 10 L. Add the 5% allowance: 10 × (1 + 5/100) = 10.5 L.
Diagram of this result
Coverage on the label is for one coat on a smooth, primed surface. Round the litres up to the can sizes you can buy.
The painted area, the coverage rate, the allowance factor and the litres are stated as numbers in the diagram.
Common mistakes
The coverage rate normally applies to one coat. Doubling coats doubles the volume; it does not double the coverage. Rough or absorbent surfaces may use more than the label estimate.
Assumptions and limits
Positive area and coverage up to one million in their stated units; 1–100 integer coats; 0–100% allowance. Litres are an estimate before rounding to available container sizes. No surface preparation, primer choice or drying time is inferred. Material estimates only; verify measurements, product guidance and site requirements before ordering.
Should I round up to cans?
Yes when purchasing. Divide the calculated litres by your selected container size and round up, while checking that the product is appropriate for the surface.
Method and references
Area × coats gives the total area painted; dividing by the label coverage gives litres, scaled by an explicit percentage allowance. Coverage must come from the chosen product; no standard rate is assumed.