Free tool
Paint calculator
Add each room, deduct doors and windows, and get gallons of paint and primer for the coats you need. Coverage defaults come from manufacturer product data; change them to match your product.
How it's calculated
- Wall area = 2 × (length + width) × height, for each room
- Paintable area = wall area − (doors × door size) − (windows × window size)
- Paint (gal) = paintable area × coats ÷ coverage per gallon
- Primer (gal) = paintable area × primer coats ÷ primer coverage per gallon
How to use it
- 1Add rooms. Enter each room's length, width and wall height, and how many doors and windows it has.
- 2Check opening sizes. Set the average door and window size to match the house; they're deducted from the wall area.
- 3Set coats and coverage. Enter the number of finish coats and the spread rate from your paint's data sheet.
- 4Add primer if needed. Turn on primer for new drywall, stains or big color changes, and set its coverage.
- 5Read the gallons. The calculator gives exact gallons and the number of gallon cans to buy.
Worked example
A 12 × 14 ft bedroom with 8 ft walls, one door and two windows, two coats at 400 sq ft per gallon.
- Wall area = 2 × (12 + 14) × 8 = 416 sq ft
- Paintable area = 416 − 20 − (2 × 15) = 366 sq ft
- Paint = 366 × 2 ÷ 400 = 1.83 gal
Buy 2 gallons of finish paint. With one coat of primer at 400 sq ft per gallon, add 1 gallon of primer (0.92 gal needed).
Sources
- Benjamin Moore, Regal Select Interior Paint – Matte (product page). Accessed 2026-11-03.
Coverage 400–450 sq ft per gallon; 1 or 2 recommended coats. The calculator defaults to the low end, 400 sq ft per gallon.
- Benjamin Moore, Fresh Start High-Hiding All Purpose Primer (product page). Accessed 2026-11-03.
Coverage 400–450 sq ft per gallon; 1 or 2 recommended coats. The primer default is 400 sq ft per gallon.
FAQ
Paint calculator questions
Have a question we didn't cover? Book a demo and ask a product specialist.
How many square feet does a gallon of paint cover?
Check the data sheet for the product you're using. Benjamin Moore lists Regal Select Matte at 400–450 sq ft per gallon, and premium interior paints commonly fall in a similar range. Rough, porous or patched surfaces take more, so the calculator defaults to the low end.
Do I need two coats?
Benjamin Moore lists 1 or 2 coats for Regal Select. Two coats are standard for color changes, and many painters quote two by default for an even finish.
When should I use primer?
Prime new drywall, patched or stained areas, glossy surfaces, and big color changes. The primer line here covers the full paintable area; if you're only spot-priming, enter a lower coverage or turn it off and add a quart.
What size are the door and window deductions?
They're editable. The defaults (20 sq ft per door and 15 sq ft per window) are a starting point for typical interior doors and windows; measure and change them for large openings like sliders or picture windows.
Does this include ceilings and trim?
No, it covers walls. Ceilings and trim usually take different paint; add a room with the ceiling's dimensions or estimate trim separately.
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