Paint Calculator
Estimate paint for a complete rectangular room or individual walls. Add openings, include ceilings if needed, and separate paint from a single primer coat.
Your result
How the calculation works
Room wall area = 2 × (length + width) × height. Ceiling = length × width. Deduct door and window rectangles. Paint volume = net surface × coats ÷ coverage × (1 + waste ÷ 100). Round containers upward separately for paint and primer.
Worked example
A 5 m × 4 m room with 3 m walls has 54 m² of wall area. Add a 20 m² ceiling, subtract a 2 m² door and 2 m² window, and 70 m² remains. Two coats at 10 m²/L plus 10% waste need 15.4 L, so four 5 L containers. One primer coat needs 7.7 L, or two containers.
Assumptions and limitations
Coverage is per selected litre or US gallon. A gallon here is 3.785411784 litres, not an imperial gallon. Single-wall mode uses length × height; width is used only for an included ceiling. All openings in a section share the entered dimensions. Use separate sections for different openings.
Theoretical coverage never predicts exact usage. Porous surfaces, texture, colour changes, product, roller and application technique all matter. Check the product label, sample the surface, and keep batch consistency in mind. Cost uses whole containers and excludes labour and equipment.
Common questions
Does primer replace a paint coat?
No. This calculator adds one separate primer coat while leaving the paint coat count unchanged.
Why might actual usage differ?
Coverage claims usually reflect controlled conditions. Surface absorption and application losses can materially increase usage.
Method reviewed 2026-10-07. Calculation standards · Report an issue