Paint Calculator
Running out of paint halfway through the last wall — or buying two gallons too many — usually comes down to guessing instead of measuring. This free paint calculator answers the "how much paint do I need" question properly: it works as a room paint calculator and a gallons of paint calculator in one, taking your room's length, width and ceiling height, subtracting the doors and windows you will not paint, then dividing by the coverage per gallon for the number of coats you plan. It is built for bedrooms, living rooms, hallways and whole rental turnovers where the paint run should be one trip, not three.
Frequently asked questions
How much paint do I need for a 12×12 room?
For a 12 × 12 ft room with 8 ft ceilings, the four walls total 2 × (12 + 12) × 8 = 384 sq ft. Subtract one standard door (21 sq ft) and two standard windows (15 sq ft each) and you get 333 sq ft of paintable wall. Over two coats that is 666 sq ft of coverage; at 350 sq ft per gallon you need 1.90 gallons — so buy 2 gallons. With one coat you would need about 0.95 gallons, so a single gallon would just cover it. Enter your own room above and this room paint calculator gives you the same worked numbers for any size.
Do I need one coat or two coats of paint?
Two coats is the safe default: it gives even color, hides the old color underneath and lasts longer. One coat can be enough when you are repainting the same or a very similar color over paint that is in good condition, or over a tinted primer. Plan on two coats for color changes, bare drywall (after primer), patched walls, or moving from a dark color to a light one — and if you are unsure how many gallons of paint to buy for two coats vs one, run this calculator both ways and compare.
Does this paint calculator include the ceiling?
No — this calculator covers walls only, which is how most people buy wall paint. If you also plan to paint the ceiling, work it out separately: ceiling area is simply length × width (a 12 × 12 room has a 144 sq ft ceiling), then divide by the same coverage per gallon and number of coats. Ceiling paint is usually sold separately in a flat finish, so keep its gallons apart from your wall paint total instead of adding them together.
Related tools: pouring a slab before you decorate? Work out materials with our concrete calculator, or price the job against labor with the salary to hourly calculator.