CalculatorEnter your measurements below and it works the answer out.
Area divided by coverage, plus 0% waste, rounded up to whole gallons. Enter what you measured and pick how it is sold.
The arithmetic. Work out the area, divide by what one gallon covers, add 0% waste, round up. Nothing more than that — the value of the page is the coverage figures and the waste allowance, both of which are stated here rather than hidden inside the tool.
Why the waste allowance is 0%. A gallon covers 350 to 400 square feet on a smooth sealed wall and less on anything textured, porous or previously unpainted. Two coats is the honest default: one coat only works when you are repainting the same color.
How it is sold. Paint is sold by the gallon and the quart, and there are four quarts to a gallon. Buying one gallon more than you need is cheaper than a second trip for a half-quart, and leftover paint from the same batch is what you touch up with later.
Measure the openings honestly. Deduct large openings — a garage door, a picture window, a stairwell — and ignore small ones. Cutting a sheet or a board around a normal door wastes more material than the opening saves, which is why trades quote gross area and let the waste allowance absorb it.
Round up to how it is sold. A calculator that tells you 6.3 sheets is not finished. Everything below is rounded up to whole units, because that is what you can actually buy.
Divide your area in square feet by the coverage of one gallon, then add 0% and round up. At 375 sq ft each, a 200 sq ft job needs 1.
0% is what this calculator adds. A gallon covers 350 to 400 square feet on a smooth sealed wall and less on anything textured, porous or previously unpainted. Two coats is the honest default: one coat only works when you are repainting the same color.
With 8 ft ceilings the walls are 384 sq ft. At 375 sq ft a gallon in two coats that is 768 sq ft of coverage, so 3 gallons — call it 2 gallons plus a quart if you are deducting a door and a window.
On a smooth, sealed, previously painted wall, yes. On new drywall, bare plaster, or anything textured, expect closer to 300. Primer first is what gets you back to the 400 figure on the second coat.