Paint Calculator
Enter your room or wall size, take off the doors and windows, and see exactly how many gallons of paint to buy.
Results are estimates. Coverage varies with surface texture, color change, and paint quality. Porous or previously unpainted walls may need more.
How to Measure for Paint
Paint is calculated from your total wall area, the number of coats, and how much of the wall is taken up by doors and windows.
From room dimensions
Measure the room's length, width, and wall height in feet. The calculator works out the wall area as the perimeter times the height. Count the doors and windows so they can be deducted.
From a known wall area
If you've already measured each wall, switch to the Wall area tab and enter the combined square footage. This is handy for stairwells, hallways, or a single feature wall.
Coats
Two coats is the default. Choose three if you're painting a light shade over a darker existing color.
Common Mistakes to Avoid
- Forgetting the second coat. A single coat rarely covers evenly — always plan for at least two.
- Ignoring doors and windows. In a room with several openings, not deducting them noticeably overestimates the paint.
- Skipping the ceiling. If you're painting the ceiling too, calculate it separately — it isn't included in wall area.
- Buying mixed batches later. Colors can vary slightly between mixes; buy all your paint at once and have it boxed (combined) if possible.
Frequently Asked Questions
A 12 ft × 12 ft room with 8 ft walls has about 384 sq ft of wall. After subtracting one door and two windows and applying two coats, you need roughly 2 gallons.
About 350-400 sq ft per coat. This calculator uses 350 sq ft per gallon to keep the estimate on the safe side.
Two coats is standard. Use three when painting a light color over a dark wall, or one when refreshing the same color.
Yes. Each door is about 20 sq ft and each window about 15 sq ft of un-painted area. Subtracting them keeps the estimate accurate.
A little extra is useful for touch-ups. Paint is sold in whole gallons and quarts, so rounding up usually leaves a handy reserve.