Free home project calculator
Paint Calculator
Estimate room paint from actual paintable area instead of guessing by floor size.
What this calculator does
The tool calculates wall area from perimeter × height, subtracts large openings, multiplies by coats and allowance, then divides by the coverage printed on your paint container.
Before entering numbers
Sketch the project and label every dimension with its unit. Break irregular areas into rectangles, measure each separately, and note areas that are excluded. Use finished dimensions where compaction, joints or built-up layers matter.
How to get a more reliable estimate
Measure twice from fixed reference points. When opposite sides differ, do not average blindly: the shape may be out of square and the layout may create additional cuts. For packaged materials, copy coverage and yield directly from the current product data rather than an old listing or generic rule.
Allowance is not the same as profit margin or contingency. It covers realistic cutting, breakage, spillage or pattern loss. The right percentage changes with material size, room complexity, installer experience and whether matching replacement material will be available later.
Use these checks
- Use the exact product coverage, not a universal promise.
- Include ceilings separately if they will be painted.
- Fresh drywall, rough masonry and dramatic colour changes can reduce effective coverage.
- Round purchases to available can sizes and keep a labelled touch-up quantity.
Save the inputs with the supplier quote. If the purchased quantity differs sharply from this result, ask what assumption changed: measured area, unit conversion, product coverage, layer thickness, waste or package rounding.
Related planning guides
Calculation transparency
ZHowTo calculators run in your browser and use the values shown in the form. No result is sent to a server. The method is explained above so you can reproduce the arithmetic independently or challenge an assumption.