Paint Calculator
Work out how many gallons of paint you need for any room based on dimensions, coats and coverage.
The paint calculator works out how much paint you need for any room. Enter the length, width and ceiling height, then subtract doors and windows. The calculator assumes 350 sq ft per gallon coverage (typical for interior latex), accounts for the number of coats and tells you how many whole gallons to buy. Two coats is standard for color changes and most paint jobs - one coat only works when refreshing the same color over a clean surface.
Explore all our interior finishes calculator tools, or browse the full construction & home improvement diy calculators.
Frequently asked questions
A 12 ft x 10 ft room with 8 ft ceilings has 352 sq ft of wall area. After subtracting one door and two windows, that drops to about 300 sq ft. For two coats at 350 sq ft/gallon, you need about 1.7 gallons - so buy 2 gallons to be safe.
Always plan for two coats unless you are refreshing the exact same color over a clean, primed surface. Two coats give a uniform finish, hide brush marks and last longer. A room that needs 1 gallon for one coat needs 2 gallons for two coats.
Standard interior latex covers 350-400 sq ft per gallon on smooth, primed drywall. Textured walls, porous surfaces or dark-to-light color changes reduce coverage to 250-300 sq ft per gallon. Check the can - manufacturer ratings vary.
Yes. A standard interior door is about 21 sq ft (3x7 ft). An average window is about 15 sq ft (3x5 ft). Subtract these from the wall area before calculating gallons. For very small rooms, the difference is significant - in a 10x10 bathroom, removing two windows drops the calculation by 10%.
Use primer separately if you are painting raw drywall, going light over dark, or covering stains. Many modern paints are "paint and primer in one" which works on already-painted surfaces in similar colors. For new drywall, always use a dedicated drywall primer first.