Paint Calculator
Enter your room dimensions and calculate the paint quantity and number of tins needed.
How to Calculate Paint Quantity by Square Metre?
The basic paint calculation formula is: multiply the net wall area by the number of coats, divide by the paint's coverage rate per litre, then add the waste factor. Gross wall area is calculated as 2 × (length + width) × height.
Why Should Door and Window Openings Be Deducted?
Doors and windows are not painted. If these openings are not deducted from the gross wall area, you end up buying unnecessary paint. A standard interior door is approximately 1.8 m² (0.9 × 2.1 m) and a standard window is approximately 1.2 m² (1.0 × 1.2 m). The calculator deducts these values automatically.
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 | ≈ 44.1 m² |
| Coats | 2 |
| Total paintable area | ≈ 88.2 m² |
| Coverage rate | 10 m²/L |
| Waste factor (10%) | ≈ 10% |
| Paint required | ≈ 9.7 litres |
How Many Square Metres Does 1 Litre (or 1 Kg) of Paint Cover?
Coverage depends on both product quality and the application surface. A quality interior paint on a smooth plastered surface covers 10–12 m²/L, whereas on rough, absorbent or previously painted surfaces this can drop to 7–8 m²/L.
The 'theoretical coverage' stated on paint packaging refers to a single coat on a smooth surface. Actual consumption is always higher. It is therefore safe to calculate using a coverage rate 10–15% below the theoretical figure, or to add a 10% waste factor.
For water-based paints 1 litre ≈ 1 kg is a reasonable approximation; for oil-based or solvent-based paints, density varies — calculate the litre/kg conversion from 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 |