Paint Calculator: Gallons for a Room
Work out how many gallons of paint a room needs for the number of coats you plan.
Runs in your browser. Your files never leave your device. See how to check
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How to do it
- 1Step 1: Open Paint Calculator: Gallons for a Room and add your input
Type your numbers or text, add your file, or pick the options you need. Nothing is uploaded: everything stays in your browser.
- 2Step 2: What Paint Calculator: Gallons for a Room does
Work out how many gallons of paint a room needs for the number of coats you plan.
- 3Step 3: Read the result and compare
The result appears at once. Change one value to see how the answer moves, then keep the figure that fits your case.
- 4Step 4: Copy or save it
Copy the result or download it. For an important decision, confirm it with the official source or an adviser.
About this tool
Enter the room length, width and wall height, the number of doors and windows, the coats and the coverage of your paint. The calculator subtracts the openings, adds the ceiling if you want to paint it and gives the gallons.
Formula
Wall area = perimeter × height, which is 2 × (length + width) × height. Subtract about 21 ft² for each door and 15 ft² for each window. Gallons = area × coats ÷ coverage per gallon.
Coverage
Most paints cover about 350 square feet per gallon on smooth walls; rough or porous surfaces take more. Primer coverage is similar. New drywall needs a primer coat.
Tip
Buy a little extra for touch-ups. Check the label for coverage, which varies by product.
Worked example
A 14 × 12 ft room with 8 ft walls, one door and two windows has 416 ft² of wall, 51 ft² of openings and 365 ft² to paint. Two coats at 350 ft² per gallon need 2.09 gallons.
Tips for best results
Check every box before you rely on a result, because one wrong digit changes the whole answer. Use the exact figures from your payslip, bill, certificate or contract, and keep a note of the date you calculated. Rates, thresholds and rules change from time to time, so for tax, fees and legal matters treat the output as an estimate and confirm with the official source named on this page. You can run as many scenarios as you like; nothing is saved or sent, and refreshing the page clears the boxes.
Quick facts
- Category: UK & US
- Works in your browser, no sign-up, no upload.
- Your input stays on your device.
- Available in English.
- Content last reviewed:
Frequently asked questions
How many coats?
Two for most colour changes, one if repainting a similar colour with a good paint.
Do I paint the ceiling?
Tick the box to add the ceiling area.
What coverage should I use?
The one printed on the can, usually 300 to 400 ft² per gallon.
How much for trim?
A quart usually covers the trim of a room.