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Most paint cans claim around 350–400 sq ft per gallon, but doors, windows, texture and a second coat change the real number. Enter your walls, ceiling and coats to see gallons of paint plus primer, with waste allowance included.
The formula
Paintable area = (wall perimeter × height − doors − windows) + ceiling (optional). Divide by ~350 sq ft per gallon per coat, add 10% waste, then round up — paint is sold in whole quarts and gallons. Primer follows the same math at one coat for bare drywall, patches or dark-to-light color changes.
Quick reference
| Room (8 ft ceilings) | Wall area (approx.) | One coat | Two coats |
|---|---|---|---|
| 10 × 10 ft bedroom | ~320 sq ft minus door/window | 1 gallon | 2 gallons |
| 12 × 14 ft bedroom | ~415 sq ft minus openings | 1–2 gallons | 2–3 gallons |
| 16 × 20 ft living room | ~575 sq ft minus openings | 2 gallons | 3–4 gallons |
FAQ
Do I need primer?
Yes for bare drywall, spackle patches, stains or dramatic color changes. Over clean, previously painted walls in a similar color, a two-coats paint-only job is usually fine.
Why buy extra paint?
Textured walls drink 10–20% more, and an extra quart from the same batch saves a visible mismatch on future touch-ups.
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