Free Paint Calculator
Buy the right amount of paint the first time. Enter your room size, doors and windows, and the number of coats to get gallons for walls and ceiling.
Wall paint needed
How to use the paint calculator
- Measure the room's length and width along the floor and the height from floor to ceiling.
- Count the doors and windows. Standard sizes are subtracted automatically (about 20 sq ft per door and 15 sq ft per window).
- Choose the number of coats. Two is standard for a color change; one can be enough for a refresh in the same color.
- Tick the ceiling or primer boxes if needed, and enter the price per gallon to estimate cost.
How much paint covers a room
Most interior paints cover about 350–400 square feet per gallon per coat on smooth, previously painted walls. Textured walls, rough plaster and fresh drywall drink more paint, so lower the coverage figure to 250–300 for those. The can label lists the manufacturer's coverage; use that number if you have it.
The calculator finds the wall area (the room's perimeter times its height), subtracts doors and windows, multiplies by the number of coats and divides by coverage. It then rounds up to a practical purchase: whole gallons plus quarts, since a gallon usually costs only a little more than three quarts. For large jobs, 5-gallon buckets are usually the cheapest per gallon.
Buy a little extra and keep it, labeled with the room and the date, for touch-ups. Mixing all your cans together in one bucket before you start (called boxing) keeps the color perfectly consistent from wall to wall. Primer is worth it on new drywall, patched areas, stains, and dramatic color changes such as covering a dark red with a light gray.
Need a different tool? Suggest it here — we read every message.
Frequently asked questions
How many coats of paint do I need?
Two coats for a new color or for the most even finish. One coat can work when repainting the same color in good condition. Very dark or bright colors may need three, or a tinted primer first.
How much paint for a 12×12 room?
With 8-foot ceilings, one door and two windows, about 350 sq ft of wall area: roughly 2 gallons for two coats.
Do I need to subtract doors and windows?
Yes. It keeps you from overbuying. The calculator uses about 20 sq ft per door and 15 sq ft per window.
How much is a gallon of paint?
Quality interior paint typically costs $35–$75 per gallon, with premium paints higher. Better paint often covers in fewer coats.