Enter your room dimensions, doors, windows and coats to find out exactly how many gallons of paint to buy — no more guessing at the store.
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Buying paint by guesswork almost always means an extra store trip — either you run short mid-wall with a half-dry roller, or you overbuy and end up with cans of leftover color. This calculator does the geometry for you so the number you walk in with is the number you actually need.
Rounding up to whole gallons or quarts means you finish the second coat without a mid-project supply run.
Doors and windows don't get painted, so subtracting their area keeps the estimate realistic.
Coverage rate and coat count are editable, so the result matches the actual can you're buying.
The calculator first finds your gross wall area by multiplying the room's perimeter by the wall height. It then subtracts the area taken up by doors and windows, since paint doesn't go on those surfaces. The remaining net wall area is multiplied by your number of coats, then divided by the coverage rate printed on the paint can — typically 350 to 400 sq ft per gallon for a smooth interior wall, though textured surfaces, dark color changes and unprimed drywall usually drink up more. Because paint is sold in gallons and quarts rather than arbitrary decimals, the result is rounded up rather than down at every stage: a project that needs 4.1 gallons still means buying 5, not 4, or 4.25 gallons in quart-sized increments if your store sells quarts separately. If your calculated openings ever exceed the total wall area — for example a small accent wall with an oversized window — the tool floors the paint amount at zero and flags it rather than showing a confusing negative number.
Coverage varies by paint and surface, but most products cover about 350 to 400 sq ft per coat on smooth walls. Use the coverage rate field to match the number on your paint can's label for the most accurate result.
Yes, generally. A standard interior door is about 21 sq ft and an average window about 15 sq ft, so subtracting them keeps you from buying paint for surfaces you won't paint. Both defaults are editable.
Paint is sold in gallons and quarts, not exact decimals. The exact figure shows the true math, while the quart and whole-gallon amounts round up so you don't run short mid-coat.
Two coats is standard for most color changes and gives the most even, durable finish. One coat can be enough for a close touch-up on an already similar color.
No, it estimates topcoat paint only. If you're priming bare drywall or making a big color change, estimate primer separately using the same wall area and a primer coverage rate.
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