Interior walls
Paint Calculator
Calculate paint from the full room perimeter, wall height, openings, number of coats, and the real coverage printed on your can.
How to calculate it
- Enter room dimensions and wall height.
- Subtract the combined area of large doors and windows.
- Use the manufacturer coverage rate and planned number of coats.
What the calculator is doing
Paint volume = {[(2 × (length + width) × height) − openings] × coats ÷ stated coverage} × (1 + waste %); cans = ceil(volume ÷ can size).
- Coverage is applied per coat, so doubling the coats doubles theoretical paint demand.
- Only sizable openings should be deducted; small deductions usually disappear into roller and container loss.
- Primer must be calculated separately because its coverage and number of coats differ.
Buying checklist
- Use the coverage rate printed on the chosen finish and sheen.
- Decide whether primer and ceiling paint are separate products.
- Record the number of coats recommended for the substrate.
- Keep tint labels and mix all same-color cans together when practical.
Common mistakes
Using floor area for walls
Wall demand depends on perimeter and height, not floor square footage.
Assuming label coverage is guaranteed
Texture, porosity, spraying, and dramatic color changes reduce real spread rate.
Combining primer and finish
The two products often have different coverage and should be estimated independently.
Frequently asked questions
How accurate is the coverage on a paint can?+
It is a planning figure under ideal conditions. Rough walls, spraying, absorbent surfaces, and dramatic color changes can reduce real coverage.
Should primer be included?+
Calculate primer separately using its own coverage rate. Primer and finish paint usually have different spread rates and package sizes.