Paint Calculator — gallons for a wall area

How it works

To work out how much paint to buy, start from the area you are painting, account for the number of coats, and divide by how much a gallon covers:

gallons = ⌈area × coats ÷ coverage⌉

The coverage depends on the paint and surface — labels usually quote 350 to 400 square feet per gallon for a smooth wall, less on rough or porous surfaces. It is an input here, so set it to your paint's figure. Two coats is standard for good, even color; primer counts as its own coat.

The result is rounded up to whole gallons, since you cannot buy a fraction. For the paintable area, take the wall area and subtract large openings like doors (about 20 sq ft each) and windows (about 15 sq ft) — or leave them in for a small safety margin.

Worked example

A room with 400 sq ft of wall, painted with 2 coats of paint that covers 350 sq ft/gal, needs (400 × 2) ÷ 350 = 2.3 → 3 gallons. One coat of the same paint needs ⌈400 ÷ 350⌉ = 2 gallons. A larger 800 sq ft job at 2 coats comes to ⌈1600 ÷ 350⌉ = 5 gallons.

Frequently asked questions

How much paint do I need?

Multiply the area by the number of coats and divide by the coverage per gallon, then round up: gallons = ⌈area × coats ÷ coverage⌉. For 400 sq ft at 2 coats and 350 sq ft/gal, that is 3 gallons.

How much does a gallon of paint cover?

Typically 350 to 400 square feet per gallon on a smooth, primed wall. Rough, textured or unprimed surfaces soak up more, dropping to 250–300 sq ft/gal. Use the figure on your paint can for the best estimate — it is an input here.

How many coats of paint should I apply?

Two coats is standard for durable, even coverage, especially over a color change. One coat may do for touch-ups or repainting a similar shade. Primer, when needed, counts as an extra coat and is often a different product.

How do I find the wall area to paint?

Multiply each wall's width by its height and add them up, or use the room perimeter times the ceiling height. Subtract large openings — roughly 20 sq ft per door and 15 per window — or leave them in as a small buffer.

Should I buy extra paint?

A little extra is wise for touch-ups later, and buying by the gallon already rounds up. Keep the leftover sealed and labeled; matching a color exactly again is hard, so a small reserve of the original batch is valuable.

Does this account for primer or the ceiling?

No — it sizes the paint for the wall area and coats you enter. Primer is a separate product (calculate it as its own coat), and the ceiling is a separate area; add it in or run the numbers separately.