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TNToolsNexus

Paint calculator

Work out how many gallons of paint a room needs — wall area minus doors and windows, times coats, at your can's real coverage rate. Math shown.

Wall length = the distance around everything you're painting (a 12 × 10 ft room is 44 ft). Doors count as 20 sq ft, windows as 15.

You'll need about

1.7 gallons

Buy 2 gallons to be covered.

352 sq ft of wall − 50 sq ft of doors/windows = 302 sq ft × 2 coats ÷ 350 sq ft per gallon.

Estimated on your device — no measurements are uploaded or stored.

Maintained by ToolsNexus

Answer “how much paint do I need?” with arithmetic instead of guesswork: wall area, minus standard door and window allowances, times coats, divided by your paint’s real coverage. The math prints under the result so you can sanity-check it against the can.

How to estimate paint

  1. Total wall length: add up the walls you’re painting — for a whole room that’s the perimeter (a 12 × 10 room: 44 ft).
  2. Wall height: floor to ceiling (8 ft is standard; 9–10 ft in newer builds).
  3. Count doors and windows — subtracted at 20 and 15 sq ft each.
  4. Set coats (2 is the honest default) and the coverage from your paint can (350 sq ft/gallon is the industry-standard planning number).
  5. Read the exact gallons and the buy figure, rounded up to whole cans.

The formula

gallons = (wall length × height − doors × 20 − windows × 15) × coats ÷ coverage. Ceilings are a separate job: length × width ÷ coverage per coat (that 12 × 10 ceiling adds 120 sq ft ≈ a third of a gallon per coat). Trim, doors themselves, and baseboards are usually a different product (semi-gloss) — a quart covers about 90 sq ft.

Buying strategy

Paint comes in gallons and quarts; a quart covers ~85–90 sq ft. If the exact figure lands just over a whole gallon (say 1.1), a gallon plus a quart beats two gallons — unless you want leftover for touch-ups, which is the one genuinely good reason to round up. Keep the receipt: unopened, untinted cans return; custom-tinted ones don’t. Get the wall area itself from the square footage calculator if the space is more complicated than one room.

Private by design

The estimate runs on your device as you type — no measurements leave the page, nothing is stored. Metric conversions for the label numbers live in the unit converter.

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Frequently asked questions

How much paint do I need for a 12 × 10 room?
With 8 ft ceilings: 44 ft of wall × 8 ft = 352 sq ft, minus a door (20) and two windows (30) = 302 sq ft. Two coats at 350 sq ft per gallon = 1.7 gallons — buy 2. That worked example is this calculator′s default.
What coverage number should I use?
Read the can — most interior latex paints state 350–400 sq ft per gallon per coat on smooth, primed walls. Use the low end (300–325) for textured, porous, or previously unpainted surfaces, and for strong color changes plan on the second coat regardless.
Do I really need two coats?
Almost always yes for a color change or sheen change; one coat can work when repainting the same color in the same sheen. Dramatic changes (dark over light or the reverse) may need a tinted primer plus two coats — cheaper than three coats of premium paint.
Should I subtract every door and window?
The standard allowances (20 sq ft per door, 15 per window — what this tool subtracts) keep the estimate honest without measuring each opening. Skip subtracting if you have only one small window and want margin; a slightly generous estimate beats a second trip mid-wall.
How much does a gallon of paint cover in metric?
350 sq ft per US gallon is about 8.6 m² per liter. Metric cans usually state 10–12 m²/L — the difference is marketing optimism plus surface condition, so the can′s own number wins if you have it.

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