Paint Calculator

A 12 ft x 14 ft room with 8 ft ceilings has a 52 ft perimeter, so the gross wall area is 52 x 8 = 416 sq ft. Take out one standard door (21 sq ft) and two standard windows (30 sq ft) and you are painting 365 sq ft.

Two coats means covering 730 sq ft. At 350 sq ft per gallon that is 2.09 gallons, so you buy 2 gallons and 1 quart and finish with roughly a quarter of a quart spare. Adding the ceiling (168 sq ft, 2 coats) needs about 0.96 gallons of ceiling paint, which is one gallon.

Between 250 and 400 sq ft per coat, and any site that gives you one number without a range is hiding the hard part. The spread is real: smooth, previously painted drywall gives 350 to 400, fresh primed drywall 300 to 350, knockdown texture 250 to 300, and bare masonry can drop under 200.

Paint quality shifts it too. A thick, high-solids paint spreads less far per gallon but hides in fewer coats, so cheap paint that covers 400 sq ft per gallon and needs three coats costs you more paint, not less. We default to 350 sq ft per gallon and let you change it, because your can is the authority.

Yes, and this calculator does it by count and by size rather than with a vague percentage. A door is about 21 sq ft and a window about 15 sq ft, so a normal bedroom loses 50 to 70 sq ft, which is a fifth of a gallon at two coats. It is not nothing.

Two cautions. If the openings add up to less than about 10% of the wall, subtracting them can leave you short once cutting in and roller loss are counted, which is what the touch-up allowance is for. And if you are painting the door slab itself, do not subtract it: add it to the trim line instead, counting each face separately.

Two is the honest default for almost every job, including "same color" repaints, because one coat leaves a patchy sheen even when the color looks right. Use one only for a genuine touch-up of the identical paint from the identical can.

Use three when a deep or saturated color goes over a light wall, when a light color goes over a dark wall, or with reds, oranges and clear yellows, which have weak-hiding pigments. The better fix is a tinted primer coat: it is cheaper per gallon than finish paint and turns a three-coat job into primer plus two.

Not as a coat of your finish color, no. Primer is a separate purchase and a separate calculation. Run the calculator once for your finish paint at your chosen number of coats, then run it again with the coats set to 1 and the coverage rate dropped to 200 to 300 sq ft per gallon to size the primer.

Primer covers less ground per gallon than paint on the surfaces that need it most: bare drywall, patched areas, raw wood and anything stained. That lower coverage number is not us being cautious, it is what the primer cans themselves print.

By volume, a gallon is nearly always cheaper than four quarts, and usually cheaper than three. The calculator gives you gallons plus quarts by default because it is the honest minimum, but if the answer comes out at 2 gallons plus 3 quarts, price a third gallon before you buy the quarts.

Use the "round up to whole gallons only" button to see that version. It also matters for color: every can tinted at the same time from the same base comes out matched, while a quart bought three weeks later can be visibly off on a large wall.

Trim is a length times a width, not a room area. Add up the linear feet of baseboard, casing and crown, then multiply by the average width of the molding in feet. A 4 in baseboard is 0.333 ft wide, so 52 linear feet of it is about 17 sq ft of paint.

The suggested figure in the calculator adds baseboard around the perimeter (minus door widths), roughly 17 linear ft of casing per door, and 16 per window. Doors themselves are the exception: a door slab is about 21 sq ft per face, so add 42 sq ft per door you are painting on both sides rather than treating it as trim length.

Three reasons, and none of them get explained on the sites that disagree. First, the coverage rate: some use 400 sq ft per gallon, some 250, and that alone changes the answer by 60%. Second, deductions: some subtract nothing, some subtract a flat 15%, some ask for real openings. Third, rounding: a calculator that says "1.7 gallons" has not answered the question, because nobody sells 1.7 gallons.

That is why this page shows the coverage rate as an input you control, subtracts openings by count and size, shows the arithmetic with your own numbers in it, and finishes with cans you can actually buy plus the leftover. If you disagree with an assumption, change it and watch the answer move.