The paint calculator estimates liters required for identical rectangular walls after subtracting standard door and window areas and multiplying by the number of coats. Coverage is editable to match the paint manufacturer's specification.
How to use this calculator
Enter wall length and height in meters, identical wall count, door and window counts, coats, and coverage per liter per coat. The model subtracts 2.1 m² per door and 1.5 m² per window from gross wall area.
Formula & calculation method
Paint liters = [(length × height × walls) − 2.1 × doors − 1.5 × windows] × coats / coverageNet paintable area cannot be negative. Coverage varies by surface and product, so the calculator treats it as a user-controlled assumption rather than a fixed universal rate. Results include net wall area and paint quantity.
Worked example
Four walls measuring 5 by 3 meters have 60 m² gross area. One door and two windows subtract 5.1 m², leaving 54.9 m². Two coats at 10 m² per liter require about 10.98 liters.
Why this is useful
Editable dimensions, openings, coats, and coverage make the estimate more adaptable than a single room-size rule. Showing net area lets you verify the geometry before buying paint.
Limitations to keep in mind
The estimate excludes primer, texture, color changes, overspray, waste, ceilings, trim, and irregular openings. Actual spreading rate may be lower on porous or rough surfaces, so follow product guidance and consider sensible extra allowance.
Frequently asked questions
Are door and window sizes adjustable?
This simple version uses standard allowances of 2.1 m² and 1.5 m². For unusual openings, adjust the wall inputs or calculate net area separately.
Does the result include extra paint for waste?
No. Add a reasonable contingency based on surface, application method, and product advice before purchasing.
Why does coverage matter?
Coverage converts area into liters. Using an unrealistic value can materially understate or overstate how much paint is needed.