Paint Calculator
Free paint calculator. Estimate gallons and liters of paint for walls and ceilings from room dimensions, coats, and openings. No signup.
What is a paint calculator?
A paint calculator estimates how much paint a room needs from its dimensions, coats, and openings. It returns gallons and liters — the numbers that let you buy once instead of running back to the store mid-project.
How this calculator works
- Enter room length, width, wall height, and the combined door/window area.
- Wall area = 2 × (length + width) × height, minus openings; add the ceiling if you’re painting it.
- Multiply by the number of coats — most repaints need two.
- Divide by coverage (about 350 ft² per gallon per coat) and round up.
How to use the result
- Buy the rounded-up number; paint is sold by the gallon or liter, and a partial can is better than a shortfall.
- Use two coats on walls — one coat rarely covers evenly, especially over a different colour.
- Add 10–20% for dark colours, textured walls, or unprimed drywall, which absorb more.
- Plan primer separately — bare drywall soaks up far more than finished walls.
How much paint do I need per square foot?
A gallon of quality paint covers about 350–400 ft² per coat on smooth, primed surfaces. For a 12×10 room with 8-foot walls, two doors/windows, and two coats, you’re looking at roughly 2 gallons — less than people usually estimate, because openings and the math add up differently than intuition suggests.
Common mistakes
- Forgetting to subtract openings. Doors and windows shave real area off the wall total.
- Painting only one coat. Coverage estimates assume a proper coat; one coat over a darker colour shows through.
- Using lumens or wattage logic. Paint is measured by coverage, not brightness — always think square footage.
Paint covers the surfaces that drywall sheets create, and both start from the same room measurements. If you’re planning the whole room, the lighting calculator handles the other half of “how does this room feel.”