Interior Paint Calculator
Estimate gallons for walls (and optional ceiling) after doors and windows. Units: feet. Print or copy a shopping list before you buy.
HomeFixMath — Paint shopping list
Shopping list
Enter valid measurements above to build your list.
- Interior paint (match sheen & color)
- Primer (if new drywall or big color change)
- Rollers, trays, brushes, painter’s tape
- Drop cloths / plastic
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Estimates only. Match coverage to the can label; primer is separate. Not a substitute for product instructions.
How we calculate
- Wall area = 2 × (length + width) × height − (doors × door area) − (windows × window area).
- Ceiling area = length × width when enabled; else 0.
- Painted ft² = (walls + ceiling) × coats × (1 + waste%).
- Gallons to buy = ceil(painted ft² ÷ coverage). Default coverage 350 ft²/gal — change to match your can.
Example: 12×12×8 ft room, 2 doors @ 21 ft², 2 windows @ 15 ft², 2 coats, 10% waste, no ceiling → walls ≈ 312 ft² → ~2 gallons at 350 ft²/gal.
FAQ
How much paint for a 12×12 room? With 8 ft ceilings, two doors and two windows, two coats usually needs about 2 gallons (see example).
Do I need primer? Yes on new drywall, stains, or large color changes. Buy primer separately from finish paint.
What about trim? Baseboards and door casings usually need a quart or two of trim enamel, not wall gallons.
Why round up gallons? Partial cans still leave you short on the last wall. Touch-up leftover is useful.
Estimates only. Confirm with product labels, your surface, and local practice.