Almost every paint can prints its coverage as a range. Not "400 square feet a gallon" but "250-400", or "about 350-400", or "up to 400". People read the range, take the friendly end, and buy for it. This guide takes one room and buys it at both ends of the ranges four manufacturers actually publish, so you can see what the range is worth before you decide which end to trust.
The room, measured once
A 14-by-16 foot living room with 9-foot walls. Four walls unfolded: (14 + 16 + 14 + 16) × 9 = 540 square feet of gross wall.
Subtract only the openings you measured. One door at 3 by 6 feet 9 inches is 20.25 square feet. Two windows at 3 by 4 feet are 12 each, so 24. Total 44.25.
540 − 44.25 = 495.75 square feet of wall that will actually take paint. That is the only number from the tape measure that matters from here.
Two coats, because the label says so
Benjamin Moore's data sheet for its interior finish states the condition plainly: "two coats are required; previously painted surfaces can be finished with 1 or 2 coats." Glidden puts the other common trigger on its calculator page: "Drastic color changes typically require a second coat."
Two coats turns 495.75 into 991.5 square feet to cover. Everything after this is that number divided by whatever your can claims, plus the allowance you choose. I use 10 percent, which is the calculator's default and a common figure for the tray, the cut-in brush and the touch-ups.
What the cans actually print
These are the published figures, quoted as printed, with the date each was read:
| Manufacturer | Printed coverage | Words attached to it |
|---|---|---|
| Sherwin-Williams | "A gallon of paint typically covers about 350-400 square feet" | "typically", "about" |
| Glidden (PPG) | "1 gallon of paint typically covers up to 400 sq. ft." | "up to", "on primed, smooth, non-porous surfaces" |
| Behr Premium Plus interior | "250-400 Sq. Ft. Coverage per Gallon" | a 150 square foot spread |
| Benjamin Moore 550 | "Coverage per Gallon at Recommended Film Thickness 400 – 450 Sq. Ft." | "Depending on surface texture and porosity" |
| Benjamin Moore N538 | "Coverage per Gallon at Recommended Film Thickness 350 – 400 sq. ft." | same qualifier |
Two things are worth noticing before any arithmetic. "Up to 400" is a ceiling, not an estimate: it is the number you get on primed, smooth, non-porous drywall and nowhere else. And Behr's single product prints a range 150 square feet wide, which is wider than the gap between two different brands.
The same room at four figures
991.5 square feet to cover, 10 percent allowance, rounded up to the can sizes a store actually sells:
| Coverage on the can | Gallons the math needs | What you buy |
|---|---|---|
| 250 sq ft/gal | 4.363 | 4 gallons + 2 quarts |
| 350 sq ft/gal | 3.116 | 3 gallons + 1 quart |
| 400 sq ft/gal | 2.727 | 2 gallons + 3 quarts |
| 450 sq ft/gal | 2.424 | 2 gallons + 2 quarts |
Read the first and third rows together. Both are inside the range Behr prints for one product. The same room, the same two coats, the same allowance: 4 gallons and 2 quarts at one end of that can's own range, 2 gallons and 3 quarts at the other. That is a difference of nearly two gallons, decided entirely by which end of the printed range the wall turns out to be.
No other choice in this project moves the count that far. Dropping the allowance from 10 percent to zero saves two quarts at the 250 end and one quart at each of the other three figures — real, but a fraction of what the range itself moves. Going from two coats to one halves the whole thing, and one coat is not a plan for a color change.
Where the purchase actually steps
The count does not slide, it steps, and the steps are not where you would guess. Running the same room through the calculator and moving only the coverage figure, the purchase changes at these points:
- at 397 sq ft/gal and above, the answer becomes 2 gallons plus 3 quarts
- at 364 and above, 3 gallons flat
- at 336, 312, 291, 273, 257 and 243 the same thing happens a step lower each time
A can printed "350-400" crosses two of those steps, so that one range covers three different shopping lists: 3 gallons plus 1 quart at 350, 3 gallons flat anywhere from 364 to 396, and 2 gallons plus 3 quarts at 397 and up. Note what that does to the container count — 4 containers, then 3, then 5 — even though the volume you buy falls the whole way, from 3.25 gallons to 3 to 2.75. Rounding up to whole cans is what makes the count wobble while the paint goes down. If your can prints a range that crosses one of those numbers, you do not know the count until you know which end your wall behaves like.
Which end should you buy for
Buy for the low end of your can's printed range when any of these is true, because they are the conditions the high end excludes:
- the wall is bare drywall, a fresh skim coat, or patched in more than a few places
- the surface has texture — knock-down, orange peel, or anything a roller has to push paint into
- you are changing color by more than a shade, which is Glidden's stated trigger for the second coat
- the wall has never been primed, which is the condition attached to Glidden's "up to 400"
Buy for the high end only on a previously painted, smooth, primed wall in a similar color. That is the case the top of the range describes.
The quart is the rounding tool
Sherwin-Williams publishes the other half of the arithmetic on the same page: "A quart of paint covers 100 square feet." This room's two coats are 991.5 square feet of coverage, which is 9.9 quarts — but nobody buys ten quarts. The calculator rounds the remainder up to whole cans in the sizes you tell it you can buy, which is why all four rows above end in quarts rather than in whole gallons. If your store sells gallons only, switch the can-size option and the same room rounds up to whole gallons instead.
The chain, in one line
Gross wall 540 − measured openings 44.25 = 495.75 · × 2 coats = 991.5 · × 1.10 allowance = 1,090.65 square feet to buy · ÷ the coverage printed on your can · rounded up to the cans your store sells.
Put your own room and your own label figure into the paint calculator and it runs exactly that chain. If you are not sure where to find the figure on the can, the paint coverage guide shows where it is printed and why it is a range. What does the can in your cart actually say — and which end of it is your wall?
Sources
Every figure below was read on the manufacturer's own page and is quoted as printed. The arithmetic in this article was recomputed with this site's own calculation code on 2026-09-25.
- Sherwin-Williams, paint calculator page: "A gallon of paint typically covers about 350-400 square feet"; "A quart of paint covers 100 square feet"; "A gallon of primer covers about 200-300 square feet". https://www.sherwin-williams.com/en-us/color/color-tools/paint-calculator (accessed 2026-09-09)
- Glidden (PPG), paint calculator page: "1 gallon of paint typically covers up to 400 sq. ft. on primed, smooth, non-porous surfaces."; "Drastic color changes typically require a second coat." https://www.glidden.com/paint-calculator (accessed 2026-09-09)
- Behr, Premium Plus interior product page: "250-400 Sq. Ft. Coverage per Gallon". This page returns 403 to automated requests; the figure was read on screen by the operations session and recorded as such. https://www.behr.com/products/paint/behr-premium-plus-interior (accessed 2026-09-09)
- Benjamin Moore, technical data sheet 550: "Coverage per Gallon at Recommended Film Thickness 400 – 450 Sq. Ft."; "Depending on surface texture and porosity."; "two coats are required; previously painted surfaces can be finished with 1 or 2 coats." https://media.benjaminmoore.com/WebServices/prod/assets/stage/datasheets/TDS_0550/20180731%20550%20TDS%20US%20OKF.pdf (accessed 2026-09-07)
- Benjamin Moore, technical data sheet N538: "Coverage per Gallon at Recommended Film Thickness 350 – 400 sq. ft."; same qualifier. https://media.benjaminmoore.com/WebServices/prod/assets/stage/datasheets/TDS_0538/20190204%20N538%20TDS%20US%20OKF.pdf (accessed 2026-09-07)
Numbers are a worked example for one room. Coverage figures are quoted from the pages above as of the access date; the can you buy is the source of truth. The step points are this calculator's output under its own assumptions, not manufacturer statements.