Trades
Estimate paint quantity from wall area, door/window openings, number of coats, coverage rate and waste allowance.
Calculator
Paintable area = max(0, total wall length × wall height − openings). Coated area = paintable area × coats. Litres before allowance = coated area ÷ coverage per litre. Litres with allowance = litres before allowance × (1 + allowance percent ÷ 100).
This is the method behind the answer, so the result can be checked rather than simply trusted.What-if check
Paint quantity changes quickly when surface condition or product coverage changes. Use the rows below before rounding up to real tin sizes.
| Allowance | Paint required | Note |
|---|---|---|
| 0.0% | 5.16 L | Planning comparison |
| 10.0% | 5.68 L | Current input |
| 20.0% | 6.19 L | Planning comparison |
| Coverage rate | Paint required | Change |
|---|---|---|
| 8.0 m²/L | 7.09 L | +1.42 L |
| 10.0 m²/L | 5.68 L | Current rate |
| 12.0 m²/L | 4.73 L | -0.95 L |
Visual proof
28.80 m² gross wall area − 3.00 m² openings = 25.80 m² paintable area. With 2 coats, coated area is 51.60 m².
Result: 5.68 L. Assumption: Wall dimensions are entered in metres and openings are entered in square metres.
Paintable area = max(0, total wall length × wall height − openings). Coated area = paintable area × coats. Litres before allowance = coated area ÷ coverage per litre. Litres with allowance = litres before allowance × (1 + allowance percent ÷ 100).
Total wall area = 12 × 2.4 = 28.8 m². Subtract 3 m² of openings to get 25.8 m² paintable area. Two coats require 51.6 m² of coated area. At 10 m²/L, that is 5.16 L before allowance. With 10% allowance: 5.16 × 1.10 = 5.68 L.
Master’s Tip: check the coverage rate on the exact product and surface. Bare plaster, dark-to-light colour changes, rough render and spraying can use more paint than a neat room-area estimate, so round purchase quantities up to available tin sizes after the arithmetic is visible.
Standard or basis: this page uses transparent rectangular-area and coverage-rate arithmetic in SI metric units. It does not claim a paint manufacturer warranty, surface-preparation standard or trade certification.
Methodology & Accuracy
CalculationTime pages are built around visible arithmetic: the formula, assumptions, worked example and practical limitations are shown so the result can be checked rather than simply trusted.
Paintable area = max(0, total wall length × wall height − openings). Coated area = paintable area × coats. Litres before allowance = coated area ÷ coverage per litre. Litres with allowance = litres before allowance × (1 + allowance percent ÷ 100).
Standard or basis: this page uses transparent rectangular-area and coverage-rate arithmetic in SI metric units. It does not claim a paint manufacturer warranty, surface-preparation standard or trade certification.
Where a calculator follows a named legal, trade or industry standard, that standard is cited visibly. Otherwise the page uses transparent general arithmetic and states its limits.Master’s Tip: check the coverage rate on the exact product and surface. Bare plaster, dark-to-light colour changes, rough render and spraying can use more paint than a neat room-area estimate, so round purchase quantities up to available tin sizes after the arithmetic is visible.
Calculate paintable wall area, subtract doors and windows, multiply by the number of coats, then divide by the paint coverage rate in square metres per litre.
Yes when they are significant. Enter their total area as openings to subtract so the paintable area is not overstated.
Use the coverage rate printed on the paint tin or supplier technical sheet for the product and surface. The default 10 m²/L is only a planning example.
No. It estimates wall paint only from the entered wall dimensions. Add primer, ceilings, trim or specialist coatings as separate calculations or adjust the inputs deliberately.
The allowance field lets you test extra percentage for roller loss, porous surfaces, touch-ups and colour change. Round final purchase quantities to real tin sizes after checking the product.
Paint estimating starts with measured surface area, but the real purchase quantity depends on coats, product coverage, surface condition and waste. Keeping each assumption visible helps a decorator, homeowner or estimator see why a litre number changed.
Paint is usually specified by how many square metres one litre can cover for one coat. That means the first estimate is not litres at all: it is the paintable surface area after obvious openings are removed.
A second coat normally covers the same surface again, so coated area is paintable area multiplied by the number of coats. Primer, sealer or undercoat may need a separate calculation because the product and coverage rate can differ.
Manufacturer coverage figures are planning guides, not proof that every wall will use the same amount. Porosity, texture, colour change, roller type, spray method and touch-ups can all move the final quantity.