Paint Calculator
Gallons of paint for any room — walls, ceiling, coats, and cost
2 for color changes
~350 typical; check the can
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Quick summary
Wall area is the room perimeter times ceiling height: a 12×10 ft room with 8 ft ceilings has 352 sq ft of wall. Subtract about 21 sq ft per door and 15 per window, multiply by coats, and divide by coverage (350 sq ft per gallon is standard). That example needs about 1.7 gallons for two coats — buy 2. One gallon covers a small bathroom; an average bedroom takes 2 gallons for two coats.
Reviewed by Simple Calculators TeamLast reviewed
How to use this calculator
- Enter the inputs requested by the calculator.
- Choose the units or options that match your situation and review the assumptions.
- Run or update the calculation to see the result.
- Review the result, breakdown, and formulas shown on the page.
- Check the inputs, units, dates, and limitations before saving or sharing the result.
Frequently asked questions
How much paint do I need for a 12x12 room?
With 8 ft ceilings: 384 sq ft of wall, minus a door and window leaves roughly 350 sq ft — one gallon per coat, so buy 2 gallons for the standard two coats. Add about a third of a gallon per coat if painting the ceiling.
How much does a gallon of paint cover?
Manufacturers rate most interior paints at 350–400 sq ft per gallon on smooth, primed surfaces. Textured walls, bare drywall, and dramatic color changes absorb more — plan on 250–300 sq ft effective coverage in those cases, or lower the coverage figure in the calculator.
Do I really need two coats?
Usually yes for color changes and rich colors — one coat rarely hides fully. Exceptions: repainting the same color, or premium paint-and-primer products going over a similar shade. Going dark-to-light or light-to-dark may even need a tinted primer plus two coats.
Should I round up or down on gallons?
Up, almost always. Running out mid-wall risks a visible lap line and a color-batch mismatch, while leftover paint from the same batch is exactly what you want for future touch-ups. Store it sealed and labeled with the room name.
Key terms
- Coverage Rate
- Square feet one gallon covers — 350 is the standard planning figure; check the can.
- Cutting In
- Brushwork at edges and trim before rolling — uses slightly more paint than rolling alone.
- Dye Lot / Batch
- Paint mixed at one time; separate batches of the same color can differ subtly, so buy enough at once.
Methodology, sources & limitations
This page shows the formula, assumptions, and limitations used for this estimate. Rates, thresholds, and other time-sensitive inputs can change, so verify them against the relevant official source before relying on a result.
For our review approach and the primary sources we consult, see the methodology and source policy. If you spot an outdated figure or formula, please contact us with a correction.