Paint Calculator
Find out how much paint you need for a room. Enter the dimensions, number of coats, and how many doors and windows to subtract, and get the gallons and cans required.
Paint calculator
Covers the four walls. Assumes ~350 ft² per gallon per coat, a door ≈ 21 ft², and a window ≈ 15 ft². Buy a little extra for touch-ups.
How to use it
- Enter the room length, width, and wall height in feet.
- Set the number of coats and how many doors and windows to subtract.
- Adjust the coverage if your paint's label differs from ~350 ft²/gallon.
How it's calculated
We calculate the wall area as 2 × (length + width) × height, subtract the door and window area, multiply by the number of coats, then divide by the paint's coverage (about 350 ft² per gallon) and round up to whole cans.
Frequently asked questions
- How much paint do I need for a room?
- Measure the wall area (perimeter × height), subtract doors and windows, multiply by the number of coats, then divide by the coverage (about 350 ft² per gallon). The calculator does this for you.
- How many gallons of paint per coat?
- One gallon typically covers 350–400 ft² in a single coat. A standard 12 × 10 ft room with 8 ft walls needs roughly one gallon per coat.
- Does the calculator include the ceiling?
- No — it covers the four walls. Add the ceiling area (length × width) separately if you are painting it too.
Last updated June 2026.