MeasureMaterial

Paint Calculator

Estimate paint gallons from wall length, height, openings, coats, and product coverage.

Sum of wall lengths around the room (room perimeter for four walls).

Override the default door opening area if needed.

Override the default window opening area if needed.

Use the coverage printed on your paint can or data sheet.

How to use

Enter total wall length and height, coats, door/window counts, opening sizes, and coverage from your paint label. Then calculate.

How the calculation works

Gross wall area minus openings becomes net paintable area. Multiply by coats, then divide by coverage per gallon.

Formula

wall_area = wall_length_ft × wall_height_ft; net_area = wall_area − (doors × door_area) − (windows × window_area); paint_area = net_area × coats; gallons = paint_area ÷ coverage_per_gallon

Example calculation

Walls 48 ft long × 8 ft high = 384 ft². Minus 1×21 ft² door and 2×15 ft² windows → 333 ft² net. Two coats → 666 ft². At 350 ft²/gal → 1.903 gallons (about 2.0 gallons when rounded up to 0.1).

Assumptions

  • Default coverage per gallon (ft² / gallon)

    350 ft² per gallon

    Material: paint · Key: coverage

    Many interior latex labels cite roughly 250–400 ft²/gal depending on surface and product. Use your can’s stated coverage.

    Source: Planning default — confirm with your product label or supplier quote. Not a lab or manufacturer certification.

  • Default door area (ft² / door)

    21 ft² per door

    Material: paint · Key: opening_area

    Common rough allowance (~3 ft × 7 ft). Override if your doors differ.

    Source: Planning default — confirm with your product label or supplier quote. Not a lab or manufacturer certification.

  • Default window area (ft² / window)

    15 ft² per window

    Material: paint · Key: opening_area

    Common rough allowance (~3 ft × 5 ft). Override for large picture windows.

    Source: Planning default — confirm with your product label or supplier quote. Not a lab or manufacturer certification.

  • Scope

    Walls only (ceiling/trim not included)

    Material: paint · Key: scope

    Add a separate estimate for ceilings or trim.

    Source: Product scope note

Practical notes

  • Porous or dramatic color changes often need more paint than the label’s best-case coverage.
  • Buy from the same batch when color matching matters.
  • Ceilings and trim should be estimated separately.

Limitations

  • Coverage is product- and surface-specific — never treat the default as exact.
  • Does not model primers, texture, or spray waste explicitly beyond coats/coverage inputs.
  • Planning estimate only.

FAQ

Should I round gallons up?
Yes for purchase planning. The result shows an estimated gallon quantity; buy whole cans based on available sizes.
Where do I find coverage?
On the paint can or technical data sheet. Enter that value instead of relying on the planning default.

Related calculators

Results are planning estimates. See the Calculator Disclaimer.