Wall Square Footage Calculator
Paint is bought by the wall, not by the room. Enter the wall, knock out the doors and windows with presets, and get the true paintable area — plus how much paint it actually takes.
Openings to subtract (per wall)
| Gross wall area (all walls) | — |
| Openings subtracted | — |
| Net paintable area | — |
| Net area in square meters | — |
| Paint needed — 1 coat | — |
| Paint needed — 2 coats | — |
Paint estimate assumes one gallon covers about 350 sq ft per coat (typical range 300–400 depending on the paint and surface). Preset door and window sizes are in square feet; custom openings use the wall's unit. Calculated locally in your browser.
Worked example
The defaults above describe a square 12 × 12 ft room with 8 ft ceilings — four identical 12 ft walls. Gross area is 12 × 8 × 4 = 384 sq ft. The openings are counted per wall and multiplied by the wall count: one standard door (21 sq ft) plus one standard window (15 sq ft) per wall is 36 × 4 = 144 sq ft, leaving a net paintable area of 240 sq ft. At roughly 350 sq ft per gallon per coat, that's 0.69 gallons for one coat and 1.37 for two — so two gallons covers the job with touch-up paint to spare. If your walls are not identical, set the wall count to 1 and run the tool once per wall, adding the net figures.
Measuring walls without fooling yourself
Measure length at the baseboard line and height from floor to ceiling in the middle of the wall — old houses sag, and the tallest point decides your cuts. Don't subtract baseboards or trim; painters don't, and the area is negligible. Do subtract anything you genuinely won't paint: full-height tile, mirrors, built-in shelving. A standard interior door slab is 3 × 7 ft (21 sq ft) including its frame allowance; most double-hung windows fall between 12 and 25 sq ft.
For a ceiling, it's just the room's floor area — the room calculator already has it. For vaulted ceilings, split the wall into a rectangle plus a triangle on top and use the main square footage calculator, which has a triangle shape built in.
Wall questions
How much paint do I need for a 12 × 12 room?
Four 12 ft walls at 8 ft high = 384 sq ft gross. Subtract a door (21) and two windows (30) → about 333 sq ft. At 350 sq ft per gallon per coat, that's roughly 1 gallon per coat — buy 2 gallons for two coats and you'll have touch-up paint left over.
Should I subtract windows and doors at all?
For one door and one window on a big wall it barely moves the paint order, but on small walls — bathrooms, hallways — openings can be a third of the surface. Subtracting takes ten seconds here and can save a full can.
What about primer?
Primer covers a bit less, around 200–300 sq ft per gallon, and you normally need it only on new drywall, bare wood, or over drastic color changes. Budget one coat of primer at the 1-coat figure above, rounded up.