Paint Calculator
Estimate how many gallons of paint you need based on wall area, number of coats, and coverage rate.
Estimate how many gallons of paint you need based on wall area, number of coats, and coverage rate.
How Paint Calculator Works
Wall area is multiplied by the number of coats you plan to apply, then divided by the paint's coverage rate (how many square feet one gallon covers) — the result is rounded up to the nearest quarter gallon, since paint is typically sold in fixed container sizes.
Who Uses Paint Calculator and Why
- Figuring out how many gallons to buy for a two-coat interior wall paint job.
- Estimating paint quantity for a room based on the coverage rate printed on a specific paint can.
- Comparing gallon needs between a one-coat and two-coat approach before deciding which to budget for.
Mistakes to Avoid
- Leaving the coverage rate at the 350 sq ft/gallon default when your actual paint can states a different figure — coverage varies by formulation and surface porosity, so the number printed on your specific can is more accurate than a generic average.
- Measuring only the floor area of a room instead of the actual wall area (perimeter times wall height) — floor area and wall area are unrelated numbers, and using the wrong one badly skews the paint estimate.
- Not subtracting large door and window openings from wall area on a room with several of them, which can meaningfully overestimate the amount of paint needed.
Tips for Best Results
- Always check the specific coverage rate on your chosen paint can's label rather than relying on the default — coverage can differ meaningfully between brands and finishes (flat vs. satin vs. semi-gloss).
- Since the result rounds up to the nearest quarter gallon, buying the next full gallon up (rather than a partial can) often works out more economical if a touch-up is likely later.
Fixing Common Problems
I ran out of paint before finishing the second coat. — Check whether your actual paint's coverage rate is lower than the 350 sq ft/gallon default — darker colors, textured walls, and covering a strong existing color often require closer to 250-300 sq ft/gallon and use more paint than average.
Terms Explained
Coverage rate: How many square feet one gallon of a specific paint is expected to cover in a single coat, printed on the product label.
Coat: One full application of paint over a surface — most jobs use two coats for even color and to hide the surface underneath.