EstimatorKitFree paint coverage calculator
How far a gallon actually goes on your wall
A gallon of interior latex covers 350 to 400 square feet on smooth sealed drywall and much less on anything rougher, so this starts with the rate rather than with the room: pick the surface and it divides the figure on the can by an area factor, giving 313 square feet on knockdown texture and 188 on bare concrete block. Walls, ceiling, trim and primer then come back as four separate purchases in whole quarts, gallons and 5-gallon pails.
- 100% free
- No signup
- 10 surface types
- 375 sq ft/gal default
- Quarts, gallons, pails
Measure to the ceiling line, not to the top of the base. 8' 6", 102 in and 2.6 m all read.
A door opening comes off at 21 ft² and a window at 15 ft² — actual window size — deduct real ones where known.
Ceiling and trim, which are separate cans
Add the shelf prices to see whether a pail beats gallons
These are the three numbers on the shelf edge in front of you. Nothing here ships with a price of its own.
A gallon covers this much of your wall, not of the test panel
375 sq ft
375 ft²/gal off the can, divided by the 1 area factor for smooth, previously painted. That is the whole of the difference between this page and the number on the label.
| Product | Gallons | Buy |
|---|---|---|
| Wall paint321 ft² × 2 coats ÷ 375 ft²/gal | 1.71 | 1 gal + 3 qt |
| Ceiling paint161 ft² × 2 coats ÷ 375 ft²/gal | 0.86 | 1 gal |
| Trim enamel158 ft² × 2 coats ÷ 400 ft²/gal | 0.79 | 1 gal |
The gallon column is what the arithmetic asks for and the buy column is what a store will sell you; the gap between them is the paint left in the can, which is worth keeping labeled rather than shaking out. The 87 ft² of openings that came off the wall total mostly reappeared on the trim line: a door is a hole in the wall and 55 ft² of enamel at the same time.
Where 375 comes from
1604 ft² is what a gallon covers one mil thick — a US gallon is 231 cubic inches; spread one thousandth of an inch thick that is 231,000 square inches. Multiply by 0.35 volume solids and divide by a 1.5 mil dry film and you get 374 ft², which is why cans print 350 to 400 and not a rounder figure. Any product that claims much more is either thinner on the wall or carrying more solvent.
How to work out paint coverage for a room
Set the rate, apply the surface, then read the four products off separately.
Set the coverage rate from the can, then the surface it is going on
The field prefills at 375 square feet per gallon, the middle of the 350 to 400 that interior latex prints, and it should be overwritten with whatever is on the label of the product you are actually buying. The surface selector then divides that rate: smooth previously painted wall leaves it alone, orange peel takes 10 percent, knockdown 20, a popcorn ceiling 50, and a bare unfilled block wall doubles it. Texture does not change what is in the can, it changes how much wall hides behind a square foot of elevation, which is why it is an area factor here and not a second rate.
Enter the room and the openings, and say what the color is doing
Length, width and wall height give the elevation; each door opening comes off at 21 square feet and each window at 15. The color-change buttons set the coat count and whether a primer line appears: same color is one coat, a new color of similar depth is two, light over a dark wall is two over a primer, and a deep accent color is three because deep bases carry almost no white pigment. Every one of those stays editable afterwards.
Read the four lines as four separate trips to the shelf
Wall paint, ceiling paint, trim enamel and primer come out as their own rows because they are four products in four container sizes. Each row shows the gallons the arithmetic asks for beside the whole containers a store will sell — 3.28 gallons is three gallons and two quarts, or one 5-gallon pail if your prices say so. Enter the quart, gallon and pail prices from the shelf edge and the two plans get costed against each other.
Technical specifications
| Default coverage rate | 375 sq ft per gallon, the mid-point of the 350–400 interior latex prints — editable to whatever the can says |
|---|---|
| Theoretical anchor | 1,604 sq ft per gallon at 1 mil dry film; × 0.35 volume solids ÷ 1.5 mils gives 374 |
| Surface factors | 10 surfaces from 0.95 for a Level 5 skim coat to 2.00 for bare unfilled concrete block |
| Opening deductions | 21 sq ft per door opening, 15 sq ft per window, shown as a deduction rather than folded in |
| Trim areas used | 43 sq ft per door slab, 12 sq ft per jamb and casing set, 12 sq ft per window trim set, 3 1/4 in of baseboard face |
| Primer rate | 300 sq ft per gallon before the surface factor, priced and counted as its own product |
| Container sizes | Quart, gallon and 5-gallon pail, with a cans plan and a pail plan costed side by side from your prices |
| Not targeted | The bare 'paint calculator' query — that SERP belongs to the manufacturers and this page answers the coverage question instead |
Frequently asked questions
How many square feet does a gallon of paint really cover?
Between 350 and 400 square feet on smooth, sealed, previously painted drywall, and materially less on anything else. That range is not a marketing choice: a US gallon is 231 cubic inches, which spread one thousandth of an inch thick covers 1,604 square feet, so multiplying by 35 percent volume solids and dividing by the 1.5 mil dry film a coat is specified to leave gives 374. A product claiming 500 square feet is either thinner on the wall or carrying more solvent, and both show up as a second coat you did not plan for.
Why does the coverage on the can never match what I get?
Because the figure is measured on a smooth sealed panel and your wall is not one. Sprayed orange peel adds about a tenth to the surface area hiding behind each square foot of elevation, knockdown adds a fifth, a popcorn ceiling half, and an open-face concrete block wall roughly doubles it. Application takes its own cut on top: a roller cover with a longer nap holds more paint and lays down a thicker film, and spraying without back-rolling puts a good part of the gallon into the air. The rate on the label is a ceiling, not an average.
Does the second coat use as much paint as the first?
On a properly primed wall, near enough — and that is the argument for priming rather than against it. What actually varies is absorption: bare gypsum, fresh joint compound and old flat paint all drink the first coat, so an unprimed wall can take a third more on coat one and then behave normally on coat two. A primer is cheaper per gallon than finish paint and is formulated to seal rather than to hide, so spending a gallon there saves most of a gallon of the expensive material and gives an even sheen, which is the part people notice from an angle.
Do I need a tinted primer for a deep color?
Yes, and gray is usually the right tint rather than a lighter version of the finish. Deep reds, yellows and oranges are mixed into a clear or near-clear base with very little titanium dioxide in it, which is exactly the pigment that does the hiding, so those colors go on translucent no matter how carefully they are rolled. A gray primer matched to roughly the same value as the finish gives the color something uniform to sit on and takes the job from three thin coats to two full ones. Paint stores tint primer to a recommended gray for this reason and will do it while you wait.
How much paint does trim take, and is a quart enough?
A quart covers about 100 square feet of milled trim at the 400 square feet a gallon that semi-gloss enamel states, and a typical bedroom runs past that. The arithmetic is worth doing rather than guessing: 46 linear feet of 3 1/4 inch base is 12 square feet, a painted door is 43 square feet of slab plus 12 of jamb and casing, and a window with its casing, stool and apron is about 12. Two doors and three windows in that same bedroom is 146 square feet of trim before the base, which is two coats out of a gallon and not out of a quart.
Should I buy a 5-gallon pail instead of gallons?
Buy the pail when the job needs more than about four gallons of one color and you have somewhere to store it. Pails are cheaper per gallon nearly everywhere, but they are only cheaper in total if you use enough of what is inside, and a 5-gallon pail of a custom-tinted color is not returnable. There is also a practical argument for it: everything in one pail is one tint batch, whereas four separately mixed gallons can differ enough to read as a band on a long wall unless they are boxed together in a bucket first.
Does the paint on the ceiling need to be a different product?
It needs a different sheen and usually a different rate, which is why the ceiling is its own line here. Ceiling paint is flat by design because a ceiling shows every roller lap and every drywall imperfection under raking light from a window, and flat scatters that away. Coverage differs too: the commonest US pairing is a smooth wall under a sprayed acoustic ceiling, where the wall gets 375 square feet from a gallon and the ceiling gets 250. A popcorn ceiling that has never been painted also gets exactly one pass, because a second wet coat lifts the texture off the board.
About coverage rates, and why the number on the can is optimistic
Coverage is arithmetic before it is a claim. A US gallon is 231 cubic inches, and 231 cubic inches spread one thousandth of an inch thick is 231,000 square inches — 1,604 square feet. That figure is definitional and it is the ceiling on every coverage claim ever printed. What a real product gets is that number multiplied by its volume solids, the fraction of the can that stays behind when the water leaves, and divided by the dry film thickness a coat is specified to leave. At 35 percent solids and 1.5 mils, which is an ordinary mid-range interior latex, the answer is 374 square feet, and that is where the 350 to 400 on the label comes from. It also shows what a 500 square foot claim is buying: a thinner film, fewer solids, or a test panel nothing like a wall.
The gap between the label and the job is almost entirely surface area. A square foot of elevation is a square foot of paint only if the wall is flat, and most are not: orange peel spray texture adds around a tenth, knockdown a fifth, sand-float stucco three fifths, and a popcorn ceiling half again. Bare unfilled concrete block is the extreme case at roughly double, and it is also the case where finish paint is the wrong product for the first coat — a block filler at 75 to 125 square feet per gallon is a paste whose job is to bridge the pinholes, and rolling three coats of wall paint into them instead costs more and still telegraphs. Keeping the penalty as a factor on the area rather than burying it in a lower rate means it stays arguable: if your knockdown is flatter than most, change the 1.20 and watch the gallons move. The same logic runs through the drywall calculator for the board underneath and the insulation calculator for what sits behind it, and the raw elevation figure this page starts from is what the square footage calculator produces if you would rather measure the room once and reuse the number.
The last thing worth separating is the products. A room is not one purchase; it is wall paint in an eggshell, ceiling paint in a flat, trim enamel in a semi-gloss and primer, bought in four different container sizes and in wildly different quantities. Trim is the one people misjudge, because it is measured in linear feet and paid for in square feet: a painted door is 43 square feet of slab and another 12 of jamb and casing, so two doors eat more enamel than sixty feet of baseboard does. Deep colors are the other trap, and the fix is a tinted primer rather than a third coat — the deep bases that make a strong red or yellow possible contain almost none of the titanium dioxide that does the hiding. Where the wall is going to be covered rather than coated, wallpaper is counted in drops off a bolt and behaves nothing like this, and the wall below a tiled splashback stops where the tile and its grout take over.
Where the color you picked stays
Every number on this page is worked out by JavaScript running in the tab you are reading it in. Nothing you type — measurements, quantities, the prices your supplier quoted you — is uploaded, logged or kept, which is also why the calculators carry on working on a site with no signal.
The surface, the coats and the prices you copied off the shelf edge stay in the tab as well. No store learns which color card someone in your neighborhood is pricing.