How the paint calculator works
Results are rounded to what you can actually buy: whole gallons plus quarts. If you'd need three quarts, we round up to a gallon, because a gallon usually costs about the same.
How much does a gallon of paint cover?
Most interior paint labels promise 350–400 square feet per gallon for one coat on smooth, primed drywall. Real-world coverage is lower on textured walls, bare drywall, brick or when you change from a dark color to a light one — use 250–300 in those cases.
One coat or two?
Two coats are the standard recommendation: the first coat rarely hides the old color evenly and the second gives uniform sheen. One coat can be enough when you repaint in the same color with a quality paint.
When do you need primer?
- New, unpainted drywall or patched areas
- Big color changes, especially dark to light
- Stains, water marks or glossy surfaces
Buying tips
- A 5-gallon bucket is often cheaper per gallon than four or five single gallons.
- Buy all the paint for one room at once so the tint matches.
- Keep a little extra for touch-ups — label it with the room and date.
Frequently asked questions
How many gallons of paint for a 12x12 room?
With 8 ft ceilings, one door and two windows, the walls are 333 sq ft. Two coats at 350 sq ft per gallon is 1.9 gallons — buy 2 gallons.
How much paint for a ceiling?
A ceiling's area is simply length × width. A 12×12 ceiling is 144 sq ft, so one coat takes under half a gallon; two coats about 0.8 gallon.
Do I subtract doors and windows?
Yes for accurate numbers. A standard door is about 21 sq ft and a window about 15 sq ft. For rooms with very few openings, skipping this just gives you a little extra.
How much paint for trim?
Trim takes much less paint — a quart covers the baseboards and door casings of an average room.