Decorating & Walls calculator
Room Paint Calculator
Calculate paintable wall area and paint quantity from room dimensions, measured doors and windows, coat count and the paint's stated coverage.
Calculate paintable wall area and paint quantity from room dimensions, measured doors and windows, coat count and the paint's stated coverage. Start with measurements from the actual job and use manufacturer or supplier figures wherever the form asks for coverage, yield, density, spacing or pack size. Watch openings, coats and paint coverage in particular. Measure openings rather than assuming a standard size, and use the coverage rate from the paint you intend to buy.
What you need to enter
The Room Paint Calculator uses the following project information to calculate the result.
- Room length
- Room width
- Room height
- Doors
- Windows
- Number of coats
- Coverage per litre
Calculator result
Paintable wall area and litres required
How the Room Paint Calculator works
The Room Paint Calculator estimates paintable wall area and litres required from this relationship: perimeter × height minus openings, then coats ÷ coverage. Because the page is designed for paint for all four room walls after allowing for doors and windows, the calculation depends especially on openings, coats and paint coverage. Metric and imperial entries are normalised before the arithmetic so equivalent measurements produce equivalent results.
Room Paint Calculator worked example
Room Paint Calculator example: For a 4.0 m × 3.5 m room with 2.4 m walls, one standard door, one 1.5 m² window, two coats and paint covering 10 m²/L, first calculate the wall area, subtract the measured openings, then divide the two-coat area by the stated coverage rate. The final litres should be rounded to sensible tin sizes. The important sense-check is openings, coats and paint coverage, because that can move the real requirement away from the neat theoretical result.
Important calculation assumptions
For paint for all four room walls after allowing for doors and windows, measure openings rather than assuming a standard size, and use the coverage rate from the paint you intend to buy.
Frequently asked questions
How do I set up accurate inputs for the Room Paint Calculator?
Start with the real project rather than nominal dimensions. Measure the room length, width and wall height, then use the real sizes of doors and windows rather than assumed standard openings. That gives the Room Paint Calculator the inputs it needs for paint for all four room walls after allowing for doors and windows.
What should I verify about openings, coats and paint coverage before trusting the Room Paint Calculator?
Measure openings rather than assuming a standard size, and use the coverage rate from the paint you intend to buy. For the Room Paint Calculator, that is the main reason to verify openings, coats and paint coverage.
What should I check before buying from the Room Paint Calculator result?
Once the Room Paint Calculator has produced a result, round litres or gallons up to practical tin sizes after checking the exact paint's coverage. If walls vary greatly in porosity or colour change, keep an additional margin.