Estimate wall paint by area, coats and can size
Work from wall area to litres, then round to purchasable cans using the product’s stated coverage.
Calculate the wall area
For a rectangular room 5 m long, 4 m wide and 2.5 m high, wall area is 2 × (5 + 4) × 2.5 = 45 m². This covers the four walls, not the ceiling. Check the calculator’s scope before adding other surfaces.
Subtract openings consistently
If doors and windows account for 5 m², the net wall area is 40 m². Keep measurements in compatible units and do not subtract the same opening twice. Openings cannot exceed the total wall area.
Compare the example
40 m² net walls, 10 m² per litre per coat, 10% allowance, 2.5-litre cans
| Coats | Litres before allowance | Litres with allowance | Whole cans |
|---|---|---|---|
| 1 | 4 | 4.4 | 2 |
| 2 | 8 | 8.8 | 4 |
| 3 | 12 | 13.2 | 6 |
On a small screen, scroll the table sideways if needed.
Try this in the calculator
Enter a 5 m × 4 m room, height 2.5 m and 5 m² of openings. Use two coats, coverage 10, allowance 10% and can size 2.5 litres to reproduce four cans. Confirm the actual product coverage separately.
Try the example ↗Account for coats and coverage
For two coats and a hypothetical product coverage of 10 m² per litre per coat, the liquid requirement is 40 × 2 ÷ 10 = 8 litres. Use coverage information for the actual product and surface; the example does not guarantee how far a paint will spread.
Add allowance before rounding cans
With a chosen 10% allowance, 8 litres becomes 8.8 litres. If cans hold 2.5 litres, 8.8 ÷ 2.5 = 3.52, so four cans provide 10 litres. Rounding litres down before calculating cans can create a shortfall.
Review surfaces and separate materials
Primer, ceilings, trim and special finishes may need their own estimates. Surface condition and application can change actual consumption. Use the calculator for the measured area and stated inputs, then confirm the product system and quantity with the supplier.