Paint Calculator
Estimate how many gallons of paint you need from square footage, coat count, openings and the coverage stated for the exact product you plan to use.
Compare two product options using your calculated requirement
Enter the coverage and current price for two paints you are considering. The comparison applies both options to the same coated area from your calculation and shows the whole-gallon purchase total.
Coated area to cover: Run or update the calculator above.
This comparison uses only the coverage/yield and price values you enter. It does not rank brands, fetch retailer data, include tax or delivery, or replace product specifications.
Continue your project estimate
Estimate interior painting cost →How the estimate works
The calculator subtracts entered openings, multiplies the remaining area by the number of coats, and divides that coated area by the product coverage you enter. Exact gallons and a rounded whole-gallon purchase estimate are shown separately.
Keep product coverage visible
Coverage can vary by coating, substrate, porosity, texture, color change and application method, so ProjectCalcWorks does not hide a universal square-foot-per-gallon assumption. Use the specification for the exact product and verify the result against the package size available to you.
If a label or technical sheet gives a range rather than a single number, use the value that best matches the surface you are painting. New drywall, rough masonry, textured surfaces and dramatic color changes can behave differently from a smooth previously painted wall.
How many gallons of paint per square foot?
Paint is normally specified as square feet covered per gallon, not gallons per square foot. To estimate gallons, divide the total coated area by the coverage printed for the exact paint you plan to use.
gallons needed = coated area (ft²) ÷ product coverage (ft² per gallon)
For example, 800 square feet of coated area at a stated 400 ft² per gallon equals 2 gallons mathematically. Surface texture, porosity, application method and color change can reduce real coverage, so use the product label or technical sheet rather than a universal coverage assumption.
How to measure paintable wall area
For a single wall, multiply wall length by wall height. For several walls, calculate each wall separately and add the areas together. Then subtract doors, windows or other openings that will not receive paint. If you already know the total paintable square footage, enter it directly instead of reconstructing the dimensions.
Ceilings, trim, doors and cabinets often use different coatings or coverage rates. Treat those surfaces as separate paint calculations when the product or application changes.
One coat, two coats and primer
The number of coats directly multiplies the coated area, so it stays as an explicit input. A second finish coat can materially change the purchase quantity even when the room dimensions do not change.
Primer is not automatically counted as another coat of finish paint. If primer has a different coverage rate, calculate it separately using the primer specification. The same applies to specialty coatings, masonry paint, exterior coatings and products with unusual application requirements.
Exact gallons versus whole-gallon purchasing
The calculator shows the mathematical gallon requirement and then rounds upward to a whole-gallon purchase estimate. That makes the math transparent, but stores may sell quarts, one-gallon cans, five-gallon pails or other combinations. Compare the exact requirement with the package sizes and prices actually available before ordering.
If you are buying multiple containers or colors, keep each color area separate. Leftover paint from one color cannot usually offset a shortage in another.
Example paint calculation
Suppose a project has 450 square feet of net paintable wall area, requires two coats and the selected paint is rated for 400 square feet per gallon. The coated area is 900 square feet. Dividing 900 by 400 gives 2.25 gallons, so a simple whole-gallon estimate would be 3 gallons before considering alternative container sizes.
This example illustrates why area, coat count and product coverage are kept separate: changing any one of them changes the result.
Convert square feet to gallons of paint
The direct conversion is gallons = coated square feet ÷ coverage per gallon. “Coated square feet” means the paintable area multiplied by the number of coats. If the product label says 400 sq ft per gallon, 800 coated sq ft requires 2.00 gallons before rounding to the container sizes you can actually buy.
To work the other direction, use covered square feet = gallons × coverage per gallon. At a stated 350 sq ft per gallon, 2 gallons represent 700 coated sq ft. That could mean about 700 sq ft for one coat or about 350 sq ft for two coats.
| Product coverage | 1 gallon | 2 gallons | 5 gallons |
|---|---|---|---|
| 300 sq ft/gal | 300 coated sq ft | 600 coated sq ft | 1,500 coated sq ft |
| 350 sq ft/gal | 350 coated sq ft | 700 coated sq ft | 1,750 coated sq ft |
| 400 sq ft/gal | 400 coated sq ft | 800 coated sq ft | 2,000 coated sq ft |
These rows are conversion examples, not universal paint-yield claims. Use the coverage stated for the exact coating and surface conditions you plan to use.
Related calculators
2,000-sq-ft paint example · Drywall Calculator · Insulation Calculator
Separate wall paint from ceiling paint
See a whole-gallon purchase worked from two paints, different coat counts and different quoted coverages instead of pooling unlike products.
Applying wall and ceiling paint calculations to a bedroom
Follow a 12 by 14 ft room example that keeps wall paint, ceiling paint and flooring cartons in separate material orders, then adds installation and repair costs.
Related tools for this project
Send this calculator to a homeowner, contractor or DIY partner
Share the canonical ProjectCalcWorks link without an account or signup requirement.