Painting Calculators
Buy the right amount of paint — no half-empty cans, no mid-job runs to the store. Our paint calculators estimate gallons or liters from your room size, number of coats, and openings. Use the tools and guides below to plan interior and exterior painting projects.
Painting calculators
What you can estimate
- Gallons or liters of paint by room
- Coverage for one, two, or three coats
- Wall area minus doors and windows
- Paint cost for the project
How much paint do you really need?
A gallon of paint covers about 350 square feet in one coat on a smooth surface — less on rough or porous walls. To estimate a room, add up the wall area (perimeter × ceiling height), subtract large openings like doors and windows, multiply by the number of coats, and divide by 350. Most jobs need two coats for even color and durability, especially over fresh drywall or a big color change.
Our paint calculators run those numbers for you and add a cost estimate, so you can buy the right number of cans the first time instead of guessing at the store.
Interior vs exterior painting costs
Exterior work costs more per square foot than interior because of prep, height, and the more durable paint required. Understanding the ranges helps you budget and compare quotes.
| Project | Typical cost | Notes |
|---|---|---|
| Interior room | $300 – $800 | Walls, ceiling, trim |
| Whole interior (avg home) | $2,000 – $6,000 | Depends on square footage |
| Exterior (avg 2-story home) | $3,000 – $10,000 | Prep and height add cost |
| Paint material | $25 – $60 / gallon | Quality affects coverage & life |
Tips for a better paint estimate
- Plan for two coats — one coat rarely gives even coverage.
- Rough or textured surfaces reduce coverage; buy a little extra.
- Don't forget primer on bare drywall, patches, or drastic color changes.
- Keep leftover paint labeled for touch-ups down the road.