Paint Calculator
Enter your room dimensions to see how much paint and how many tins you need.
How to Calculate Paint Quantity by Square Metre?
Multiply the net wall area by the number of coats, divide by the paint's coverage per litre, then add the waste factor. Gross wall area is 2 × (Length + Width) × Height.
Why Should Door and Window Openings Be Deducted?
Doors and windows are not painted. If you don't subtract them from the gross wall area, you buy more paint than you need. A standard interior door is about 1.8 m² (0.9 × 2.1 m) and a standard window about 1.2 m² (1.0 × 1.2 m). The calculator subtracts these for you.
Example Scenario
A standard room measuring 5×4 m with 2.70 m ceiling, 1 door and 2 windows:
| Parameter | Value |
|---|---|
| Room length | 5 m |
| Room width | 4 m |
| Ceiling height | 2.70 m |
| Number of doors | 1 (1.8 m²) |
| Number of windows | 2 (2.4 m²) |
| Net wall area | 44.4 m² (48.6 − 4.2) |
| Coats | 2 |
| Total paintable area | 88.8 m² |
| Coverage rate | 10 m²/L |
| Waste factor (10%) | ≈ 10% |
| Paint required | ≈ 9.8 litres (88.8 ÷ 10 × 1.1) |
How Many Square Metres Does 1 Litre (or 1 Kg) of Paint Cover?
Coverage depends on both the product and the surface. A good interior paint on smooth plaster covers 10–12 m²/L; on rough, absorbent or previously painted surfaces this can drop to 7–8 m²/L.
The 'theoretical coverage' on paint packaging is for a single coat on a smooth surface. Actual use is always higher, so it is safer to calculate with a coverage 10–15% below the stated figure, or to add a 10% waste factor.
For water-based paints, 1 litre ≈ 1 kg is a reasonable approximation. Oil-based and solvent-based paints have a different density, so convert litres to kg using the density (g/L) on the label.
Paint Consumption Differences by Paint Type
Each paint type has a different coverage rate. The table below shows the coverage range to use in your calculation.
| Paint Type | Coverage Rate | Notes |
|---|---|---|
| Interior Paint (Matt) | 8–12 m²/L | Standard wall applications |
| Interior Paint (Silk/Satin) | 10–13 m²/L | Less absorbent, smooth surface |
| Ceiling Paint | 6–10 m²/L | Usually one coat is sufficient |
| Exterior Paint | 5–9 m²/L | Rough surface, weather conditions |
| Primer | 6–9 m²/L | New plaster / colour change |
| Wood Paint (Water-based) | 10–14 m²/L | Smooth wood surfaces |