Free home project tool
FixCalcPaint calculator: how much paint do I need?
Enter the room dimensions, subtract standard doors and windows, then account for coats, coverage, and an extra allowance. The result works in metric or imperial units.
Estimate paint for one rectangular room
Use the coverage printed on your paint label when you have it. Manufacturer guidance should take priority over the default value below.
How the paint estimate works
The calculator finds the area of four walls using 2 × (length + width) × wall height. It subtracts a standard allowance for each door and window, adds the ceiling when selected, multiplies the area by the number of coats and allowance, then divides by the coverage rate.
Metric estimates use 1.9 m² for a standard door and 1.4 m² for a standard window. Imperial estimates use 21 sq ft and 15 sq ft. For unusually large openings, calculate the wall area manually or use FixCalc with your project measurements.
Calculation method reviewed August 29, 2026.
Working on the floor or walls? Use the free tile calculator.
Before you buy paint
- Check the coverage on the exact product label
- Allow for porous, textured, repaired, or unprimed surfaces
- Consider an extra coat for major colour changes
- Keep enough matching paint for touch-ups
Worked example
A 3 m × 4 m room with 2.4 m walls, one standard door, two windows, two coats, 10 m²/L coverage, and a 10% allowance needs approximately 6.36 L. The calculator rounds that up to 6.5 L.
Plan the whole project in FixCalc.
Save paint, tile, and flooring estimates, package counts, costs, and shopping lists.
