Paint Calculator
Tell us what you’re painting and we’ll estimate how much paint you should buy.
How we measure a room
Measure the length and width of the floor, corner to corner, and the wall height floor to ceiling. Don’t subtract for furniture or closets — paint goes behind them eventually.
How we calculated it
We measure your walls the way a painter would: the room’s perimeter times the wall height gives the gross wall area, then we subtract a standard allowance for each door (20 sq. ft.) and window (15 sq. ft.). Multiply by your number of coats, divide by the paint’s coverage rate, and round up to whole gallons.
Things that can change your result
- Bold color changes and drastic light-to-dark switches usually need an extra coat.
- Porous or textured surfaces (fresh drywall, stucco) soak up more paint than the label suggests.
- Coverage rates vary between brands and finishes — check the can, then adjust the advanced setting.
- Ceilings, trim, and doors need their own paint and aren’t part of this estimate.
Buying tips
- Buy all your gallons at once and have the store shake them together — tint can vary between batches.
- One gallon short is two trips to the store. When the math says 1.9, that’s a 2-gallon project.
- Keep the leftover quart for touch-ups; note the color code on the lid.
Common mistakes
- Forgetting the second coat — most colors need two.
- Measuring individual walls and mis-adding — measure the room instead.
- Using the can’s best-case coverage on a textured wall.
Frequently asked questions
How much paint do I need for a 12×12 room?
With 8-foot walls, one door, and two windows, a 12×12 room is about 334 sq. ft. of paintable wall. At two coats and 350 sq. ft. per gallon, that’s just under 2 gallons — buy 2.
Does the estimate include the ceiling?
No — walls only. Ceilings are usually a different paint (flat, and often a different color), so estimate them separately: length × width ÷ coverage rate.
What if my room isn’t a rectangle?
Break it into rectangles, run the calculator for each, and add the results — or use the longest and widest points to stay on the safe side.