Paint Calculator
Wall and room estimator
Enter surfaces, openings, and paint coverage
Result
Calculation summary
Enter values to see the result
Paintable surface preview
Room wall coverage
How to use this calculator
- 1Choose a whole room, a single wall, or multiple walls and enter the measured dimensions.
- 2Add doors, windows, or custom openings that should not be painted.
- 3Set the number of coats, manufacturer coverage rate, allowance, and container size.
Formula
Paint = ((gross wall area − openings) × coats ÷ coverage) × (1 + allowance ÷ 100)
Room mode uses perimeter × wall height. Single and multi-wall modes total rectangular wall areas before subtracting openings.
Calculation steps
- Validate wall, room, opening, coverage, coat, allowance, and container inputs.
- Convert all dimensions to meters and calculate the gross wall area.
- Subtract the combined area of doors, windows, and custom openings without allowing a negative result.
- Multiply the net paintable area by the number of coats and divide by the selected coverage rate.
- Apply the allowance, then divide by container size and round up to whole containers.
Worked example
A 5 m × 4 m room with 2.8 m walls has 50.4 m² of wall area. At two coats, 10 m²/L coverage, and 10% allowance, it needs about 11.088 L, or three 5 L containers.
Assumptions
- Rooms are rectangular and use the full perimeter multiplied by a uniform wall height.
- Walls, doors, and windows are rectangular and measured to their finished boundaries.
- The same paint, coat count, and coverage rate apply to every included surface.
- Coverage is the manufacturer-stated spreading rate for one coat under the relevant surface conditions.
- Container counts are rounded up and can exceed the calculated liquid requirement.
Sources
Frequently asked questions
How do I calculate wall area for a room?
Add the room length and width, multiply by two to get the perimeter, and multiply the perimeter by wall height.
Should I subtract doors and windows?
Subtract openings that will not be painted. Small openings may be left in the estimate when their area helps cover touch-ups and application losses.
Where do I find the paint coverage rate?
Use the coverage or spreading-rate figure printed by the manufacturer on the product label or technical data sheet.
Why does the calculator multiply the area by the coat count?
Coverage rates normally describe one coat. Painting the same surface twice consumes approximately twice the paint before allowance.
Does the result include primer or ceiling paint?
No. Calculate primers, ceilings, trim, or products with different coverage rates as separate projects.