How many coats of paint do I need?

Two coats is standard for an even finish and full color. One coat may be enough when repainting a similar color; three coats can be needed for deep colors or when covering a much darker existing color.

Paint Calculator — How Much Paint Do I Need? (Free)

Q: How much does a gallon of paint cover?

One gallon of interior wall paint covers roughly 350 square feet in a single coat on a smooth, primed surface. Rough or unprimed surfaces absorb more, reducing coverage to about 250–300 square feet.

Q: Should I subtract doors and windows?

Yes. A standard door is about 21 sq ft and a standard window about 15 sq ft. Subtracting them avoids over-buying, though many people leave a small buffer for touch-ups.

How to calculate how much paint you need

The math behind a paint estimate is simple once you have the wall area:

Find the wall area. For a rectangular room, that is the perimeter times the ceiling height: 2 × (length + width) × height. Add the ceiling (length × width) if you are painting it too.
Subtract openings. Take out doors (~21 sq ft each) and windows (~15 sq ft each) that will not be painted.
Multiply by coats. Most jobs need two coats for an even, full-color finish.
Divide by coverage. A gallon covers about 350 sq ft per coat on smooth, primed walls, so divide your total area by 350 (or by your paint's stated coverage).

How much does a gallon of paint cover?

A gallon of interior wall paint covers roughly 350 square feet in one coat on a smooth, primed surface. Textured, porous, or unprimed surfaces drink more paint — expect closer to 250–300 sq ft. In metric terms, one liter covers about 11 square meters per coat.

How many coats of paint?

Two coats is the reliable default. You may get away with one when repainting a similar shade over a sound surface, while deep or saturated colors — and any big jump from dark to light — often need three. This calculator lets you set the coat count directly.

What this calculator assumes

Standard door = 21 sq ft (1.95 m²); standard window = 15 sq ft (1.4 m²).
Default coverage = 350 sq ft/gal (11 m²/L); adjust it to match your paint can's label.
Results are rounded up to whole cans, since paint is sold by the can.

Frequently asked questions

Should I subtract doors and windows?

Yes, if you want a tight estimate — a door is about 21 sq ft and a window about 15 sq ft. Many painters leave them in as a built-in buffer for touch-ups. Either approach is fine; just be consistent.

How much extra paint should I buy?

Around 10% extra is sensible. It covers spills, a heavier-than-expected second coat, and — importantly — leaves matched paint for future touch-ups from the same batch.

Does primer count?

Primer is a separate product with its own coverage (often 200–300 sq ft/gal). If you are priming bare drywall or making a big color change, calculate primer as one additional coat at its own coverage rate.

What about ceilings and trim?

Tick "Also paint the ceiling" to include it. Trim, doors, and baseboards use a different paint and very little of it — usually under a quart per average room — so they are estimated separately.