Calculators › Paint calculator

Paint calculator

Room size in, gallons and quarts out. Doors and windows are subtracted, the result is rounded up to what you can actually buy, and you won't be left with three spare cans.

How it works

Worked example

A 12 × 12 ft bedroom with 8 ft walls, one door and two windows has 384 − 21 − 30 = 333 sq ft of wall. Two coats at 350 sq ft per gallon need 1.90 gallons, so you buy 2 gallons.

Tips before you buy

Dark-to-light color changes, fresh drywall and rough surfaces like textured plaster or brick soak up more paint. Use the low end of the can's coverage figure (or 300) for those, and plan a primer coat. Trim and doors are usually painted separately in semi-gloss: a quart covers most rooms' trim.

Common questions

How much paint do I need for a 12x12 room?

With 8 ft walls, one door and two windows, about 333 sq ft of wall. Two coats at 350 sq ft per gallon need about 1.9 gallons, so buy 2 gallons. Add about 0.8 gallon (1 gallon) for the ceiling.

How many square feet does a gallon of paint cover?

Most interior wall paints say 350–400 sq ft per gallon on smooth, primed walls. Rough or porous surfaces get less, often 250–300.

Do I need two coats of paint?

Usually yes. Two coats give even color and sheen. One coat can work when repainting the same color in good condition.

More project calculators

Estimates for planning only. Product coverage and yields vary, so check the label. Last checked 2026-10-22.