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Paint Calculator

Work out how much paint you need for a room. Enter the room size, wall height, doors, windows, and number of coats to get the paintable area and gallons required — with a purchase recommendation in gallons and quarts.

Updated 2026-09-20
Room
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ft
ft
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Counted at 21 ft² each

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Counted at 15 ft² each

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ft²

Textured or unprimed: 250–300

One coat or two?

Plan on two coats for any color change, any dark or saturated color, and any wall that's seen a few years of life. One coat only holds up when you're repainting a similar light color on a wall in good condition. Going from dark to light — or painting raw drywall or patched areas — add a dedicated primer first; it's cheaper than a third coat of finish paint.

Coverage is the variable that matters

The 350 sq ft per gallon default assumes smooth, primed walls. Textured walls, porous surfaces, and first coats on new drywall absorb more — drop the coverage to 250–300 and the gallons adjust instantly. Premium one-coat paints claim higher coverage, but two thin coats almost always look better than one thick one.

Worked example

A 12 × 10 ft room with 8-ft ceilings has 44 linear feet of wall, so 44 × 8 = 352 sq ft. Subtract one door (21 sq ft) and one window (15 sq ft) for about 316 sq ft of paintable wall. At 350 sq ft per gallon and two coats, that's 632 ÷ 350 ≈ 1.8 gallons — buy 2 gallons.

Round up on purpose

The purchase recommendation rounds up to the next quart, and that's deliberate: you want leftover paint from the same batch for touch-ups, because even the same color mixed later can dry slightly differently. If the recommendation lands on 3 quarts, buying a full gallon is usually cheaper anyway.

Paint to buy
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Rounded up to the next quart
Wall area
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Deducted for openings
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Ceiling area
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Paintable area
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Area × coats
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Exact amount required
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Primer for raw drywall or big color changes is extra.

Common questions

How much paint do I need for a room?

Measure the perimeter, multiply by wall height, subtract the doors and windows, then multiply by the number of coats and divide by 350 sq ft per gallon. A 12 ft × 12 ft room with 8 ft walls is 384 sq ft of wall; minus one door (21 sq ft) and one window (15 sq ft) leaves 348 sq ft, and two coats needs about 2 gallons.

How much paint do I need for a room?

How much does a gallon of paint cover?

About 350 square feet for one coat on smooth, previously painted drywall. Manufacturers quote 250 to 400 sq ft per gallon; textured, porous, or unprimed surfaces drink more, so use the low end of the range. You can change the coverage figure in the calculator to match the can.

How many gallons of paint per square foot?

About 0.003 gallons per square foot per coat, since one gallon covers roughly 350 sq ft. Divide your wall area by 350 for gallons per coat: 500 sq ft is about 1.4 gallons per coat, or just under 3 gallons for two coats.

How many gallons of paint do I need for 1,000 square feet?

Roughly 3 gallons per coat at 350 sq ft per gallon, so about 6 gallons for two coats. Buying a single 5-gallon bucket for a job that size also keeps the color consistent across the whole room.

Do I need two coats of paint?

Plan on two coats for almost any repaint. One coat only works when the new color is very close to the old one and the surface is in good shape; big color changes, going light over dark, and bare or patched drywall need two coats over primer.

Does the calculator include the ceiling?

Only if you turn on the ceiling option, which adds room length × width to the paintable area. Ceilings are usually painted with a separate flat ceiling paint, so buy that gallonage separately from the wall color.

Should I subtract doors and windows?

Yes, for anything larger than a small window — the calculator deducts 21 sq ft per door and 15 sq ft per window. Leaving them in is a reasonable safety margin on a single small room, but on a whole floor it can cost you an extra gallon or two.

How this is calculated

Method
Wall area = 2 × (room length + room width) × wall height — the full perimeter of the room.
Paintable area = wall area − (doors × 21 ft²) − (windows × 15 ft²), plus the ceiling (length × width) when included.
Total area = paintable area × number of coats. Gallons = total area ÷ coverage per gallon (default 350 ft²/gal).
The purchase recommendation rounds up to the next quart and expresses it as whole gallons plus quarts.
Assumptions
  • A standard door is counted as 21 ft² (3 × 7 ft) and an average window as 15 ft² (3 × 5 ft). Adjust the counts if your openings are unusual.
  • 350 ft² per gallon assumes one coat on smooth, primed walls. Textured, porous, or unprimed surfaces cover 250–300 ft²/gal — lower the coverage value for those.
  • Two coats is the norm for a color change or a rich finish; one coat only works when repainting a similar color.
  • Dark-to-light changes and raw drywall usually need a separate primer, which this tool does not include.
Sources
  • Manufacturer coverage specifications (e.g. Sherwin-Williams, Behr) — Published coverage of 250–400 ft² per gallon depending on surface; 350 ft²/gal is the common planning figure.
Methodology reviewed 2026-09-20 · See our methodology for how we build and test calculators.
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