Paint Calculator
Paint needed
3 gallons
380 square feet of wall, 2 coats — 2.17 gallons of actual coverage.
- Wall area before openings
- 416 sq ft
- 1 door and 1 window
- −36 sq ft
- Or in quarts
- 9
- Or mixed, with least left over
- 2 gallons and 1 quart
Coverage assumes 350 square feet per gallon per coat, the usual figure on a tin. Porous, textured or previously unpainted surfaces drink more; a second coat always goes further than the first.
How this is calculated
Wall area is the perimeter of the room times the ceiling height, which is twice the length plus twice the width, all multiplied by how tall the walls are. Doors and windows come off that, at roughly twenty-one and fifteen square feet each, because paint does not go on glass. Multiply what is left by the number of coats and divide by the coverage on the tin, which is usually about three hundred and fifty square feet per gallon per coat. Paint is the one material on this site where buying the next size up costs real money rather than leaving a spare bag in the garage, so the quart figure matters: a job needing 1.09 gallons is two gallons if you only buy gallons, and most of the second one dries out in the tin before you ever open it again. A gallon plus a quart covers the same job with far less waste and usually less money. That is also why no waste allowance is added here — the coverage figure on the tin already assumes normal application, and adding a further percentage on top would push you into buying paint you will not use.
Worked example
The perimeter is 52 feet, which at 8 feet tall is 416 square feet of wall. A door and a window take off 36, leaving 380. Two coats means covering 760 square feet, and at 350 to the gallon that is 2.17 gallons of actual paint — so three gallons, or two gallons and a quart if you would rather not have most of a tin left over.
Inputs: A 12 by 14 foot room with 8 foot ceilings, one door, one window, two coats
Result: 3 gallons — 380 square feet of wall needing 2.17 gallons of coverage
What this assumes
- Coverage is 350 square feet per gallon per coat. Check your tin: primers, deep colours and one-coat paints all differ, sometimes by a lot.
- Doors count as 21 square feet and windows as 15. If yours are unusual, adjust the counts up or down rather than measuring exactly — the arithmetic is not that sensitive.
- No waste allowance is added, because the coverage figure already assumes normal application. Rollers, trays and the bit left in the tin are real but small.
- This covers walls only. Ceilings, trim and doors themselves are separate jobs with separate paint, and a ceiling is simply the length times the width.
Questions
- Why does it tell me quarts as well as gallons?
- Because paint is expensive and rounding up a gallon is expensive with it. A job needing just over a gallon becomes two if gallons are all you buy, and the second tin usually dries out unopened. Buying a gallon plus a quart is closer to what you need and normally cheaper.
- Do I really need two coats?
- Usually yes over a colour change, over bare plaster, or with any strong colour. One coat is realistic only when you are refreshing the same shade on a sound surface. Two thin coats also look better than one thick one, which is what most streaking comes from.
- Should I subtract every door and window?
- Subtract the big ones. A door and a full-size window are worth taking off; a small casement is inside the margin of error on the coverage figure anyway. Overestimating slightly is the safer direction, since running out mid-wall means a visible join.
- What will the paint cost?
- Type your price for a gallon and the result card costs the whole gallons this page recommends. It deliberately does not cost the mixed gallons-and-quarts option, because a quart carries a different price per gallon that you have not been asked for, and guessing it would understate what you actually pay. The price is yours, never ours.