Finish calculator
Calculate wall and ceiling area, paint gallons, coats, waste allowance, containers to buy, and estimated material cost for interior and exterior painting projects using US, metric, or mixed units.
How much paint do you need to buy?
Gallons, containers, and cost
Project inputs
Estimate
Planning purchase quantity
4containers
1 US gal each · 4 US gal (15.14 L) purchased
Rounded up to whole containers of the selected size for planning—not the exact calculated gallon requirement.
Estimated material cost
Enter a price per container to estimate material cost.
[2 × (length + width) × wall height − doors − windows + optional ceiling] × rooms
Method
Measure room walls or enter a known surface area, subtract doors and windows when needed, account for ceiling coverage, apply coats and waste allowance, divide by paint coverage, and round up to whole containers for a planning purchase quantity.
For identical rectangular rooms, wall area is 2 × (length + width) × wall height per room, multiplied by the number of rooms. Enter each dimension in its own unit if needed; the calculator converts them to feet before calculating.
When Include ceiling is checked, ceiling area is length × width per room. Uncheck it when the ceiling is not part of this paint purchase or will use a different product.
Door and window counts apply to one room. Their combined area is subtracted from gross wall area per room before ceiling area is added. Openings are not subtracted from ceiling area.
Use Surface area mode when you already know net paintable square footage. Enter the area in square feet or square meters; room dimensions, doors, windows, and ceiling options are not used in that mode.
Multiply net paintable area by the number of coats before waste allowance. Each coat covers the full net area again. Follow product and manufacturer guidance for your surface and color change.
Coverage shows how much area one gallon covers in a single coat. Prefer data from the paint can or technical sheet. The default 350 ft²/US gal is only a planning assumption.
Waste is applied to coat-adjusted area and can cover application losses, spillage, measurement variance, and touch-ups. Adjust the percentage to match your project; 10% is a starting point, not a universal rule.
Exact gallon requirement is divided by your selected container size and rounded up to a whole number of containers. Purchased volume is containers × container size, which may exceed exact requirement.
Optional cost uses only price per container times containers to buy. It excludes primer, tools, preparation, labor, delivery, taxes, and other project costs.
Common questions
Measure room walls as length, width, and wall height—or enter a surface area you already calculated—then subtract doors and windows, add ceiling area if included, multiply by the number of coats, add a waste allowance, and divide by your paint coverage rate. The calculator converts dimensions to feet, finds net paintable area, applies coats and waste, estimates exact gallons, rounds up to whole containers of your chosen size, and optionally estimates material cost. Treat the result as a planning estimate, not painting or purchasing advice.
Coverage per gallon depends on the specific paint, surface texture, application method, and whether you are applying one coat or comparing to a multi-coat project. This calculator applies coverage on a per-coat basis and multiplies net paintable area by the number of coats you enter. The default 350 ft²/US gal is only a planning assumption—use the coverage printed on the can or product data sheet when available.
In Room mode, door and window areas are subtracted from gross wall area only. Ceiling area is not reduced by openings. If you already excluded openings elsewhere, use Surface area mode with your net figure instead.
Each coat covers the full net paintable area again. The calculator multiplies net paintable area by the number of coats before applying waste allowance. Actual coat count depends on paint type, color change, surface porosity, and manufacturer instructions—two coats are not required for every project.
Include the ceiling when the same paint will cover walls and ceiling. In Room mode, ceiling area is length × width per room when Include ceiling is checked. Uncheck it when you are not painting the ceiling or when you plan a separate ceiling product outside this estimate.
Waste allowance adds a percentage to coat-adjusted area for roller and brush losses, spillage, small measurement differences, and touch-ups. The calculator defaults to 10% and allows 0% to 30%, but 10% is not necessarily right for every project. Confirm the allowance for your surface and application method.
Paint is purchased in whole containers of the size you select. The calculator keeps exact gallon requirement separate and rounds container count upward with Math.ceil so partial containers are not assumed. If exact gallons divide evenly by container size, no extra container is added. Confirm available package sizes with your retailer or manufacturer.
No. Estimated material cost multiplies your price per container by the number of containers to buy only. It does not include primer, separate ceiling or trim paint, rollers, brushes, trays, tape, drop cloths, surface preparation, repairs, labor, delivery, or taxes.
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