Finishes
Paint Calculator
Calculate paint from the surface you will coat, the number of coats and the coverage stated for your chosen product. Enter wall or ceiling area rather than floor area. The result gives a planning volume; the next step is choosing available can sizes.
The calculation
Use the actual surface area, subtract openings and enter the number of coats. Divide by the coverage per coat stated on your paint container, then apply your chosen waste allowance. Porous or textured surfaces can need more paint.
Painting 80 m² with two coats at 10 m² per litre requires 16 litres before waste. A 10% allowance increases the estimate to 17.6 litres. Choose available container sizes separately.
- Total surface area
- 80 m²
- Doors and windows to subtract
- 0 m²
- Number of coats
- 2
- Coverage per coat
- 10 m2/L
- Waste allowance
- 10 %
Paint required17.6 L
Painted surface area80 m²
Detailed guide (English)
Use the product’s coverage figure
Paint volume = (surface area − openings) × coats ÷ coverage. An optional allowance then multiplies that result by (1 + allowance percentage ÷ 100). Coverage in m²/L means square metres covered by one litre for one coat. Enter the figure from the product label or technical data sheet.
Sherwin-Williams explains that theoretical coverage can differ from practical use because of surface texture and material left on application tools. A calculator cannot judge porosity, surface condition or a strong colour change. Check the product instructions when deciding coats and coverage.
Measure walls and ceilings separately
For a rectangular room, wall area before openings is 2 × (length + width) × wall height. Ceiling area is length × width. Add only the surfaces receiving the same paint system. Doors, trim and ceilings often use different products, so separate calculations make the shopping list clearer.
Subtract the measured area of openings you will not paint. Include wall returns or other surfaces where relevant. A room’s floor area alone cannot describe its wall area because room height and perimeter also matter.
Litres and US gallons
The gallon result on this site means US liquid gallons, approximately 3.78541 litres each. An Imperial gallon is 4.54609 litres, so the two must not be treated as interchangeable. Confirm the volume printed on the can when comparing products from different markets.
Round the final volume to the available container combination after checking whether your allowance already covers touch-ups. Primer is a separate product: calculate it using its own coats and coverage rather than assuming the finish-paint result also includes primer.
Worked example
Example: two coats on 45 m²
With 45 m² of net surface, two coats and coverage of 10 m²/L, the base requirement is 45 × 2 ÷ 10 = 9 L. A chosen 10% allowance raises this to 9.9 L, approximately 2.62 US gallons. Compare that result with the product’s actual can sizes.
Common questions
Does more paint mean I need fewer coats?
No. Quantity and coat count are different. Follow the product’s application and recoat instructions; a thicker application is not automatically an acceptable substitute.
Can I enter coverage in square feet per gallon?
Use the coverage unit shown by the form. To convert ft² per US gallon to m²/L, multiply by approximately 0.02454.
Sources and references
Manufacturer and measurement references for the assumptions described above.