How much area does a gallon of paint cover?

About 350–400 sq ft in one coat on smooth, sealed drywall. On rough or porous surfaces it is much less — 200–300 on bare wood, 150–250 on stucco, 100–200 on unpainted brick. The figure on the can is a best case.

Why does my paint cover less than the label says?

The label figure is measured on a smooth, sealed surface at ideal film thickness for one coat. Texture adds real surface area, porous surfaces absorb the first coat, and a color change needs a heavier film — all of which lower your effective coverage.

How do I calculate gallons from coverage?

Use gallons = ceil(area × coats ÷ coverage), then round up. For 1,050 sq ft at two coats and 350 sq ft/gal that is ceil(2,100 ÷ 350) = 6 gallons.

Does spraying use more paint than rolling?

Yes. A sprayer loses paint to overspray and mist, so your effective coverage drops and you should plan on more gallons than a brush-and-roller job for the same area — more so outdoors in any breeze.

How paint coverage works (spread rate, texture, porosity)

Coverage is the number that turns square feet into gallons, and it is the one most people get wrong — they trust the big number on the label and under-buy. Here is what spread rate really measures, and how to pick the right figure for your surface.

By Francesco Zinghinì

What “coverage” means

Coverage, or spread rate, is the square feet one gallon covers in one coat. That last part matters: a can that says “up to 400 sq ft” means 400 sq ft at a single coat, on a smooth, sealed surface, applied at the ideal film thickness. Your two-coat job on real walls will use roughly twice the gallons for the same area — which is exactly why the quantity formula multiplies by coats: gallons = ceil(area × coats ÷ coverage).

Why the label number is the best case

The printed spread rate is measured under ideal conditions. Three things on a real job push your effective coverage below it:

Texture. A textured wall has more actual surface than its flat footprint — knockdown, orange-peel and popcorn all have hills and valleys the paint has to cover. More real area per square foot of wall means fewer square feet per gallon.
Porosity. Bare drywall, fresh joint compound, raw wood and masonry absorb paint. The first coat soaks in rather than sitting on top, so it covers far less — which is also why sealing with primer first saves finish paint.
Color and hide. A weakly pigmented color, or a big color change, needs a heavier film to hide, effectively lowering coverage.

Coverage by surface

The planning ranges a meticulous estimate uses — the same data in the coverage-by-surface reference:

Smooth, previously painted drywall (latex): 350–400 sq ft/gal
New or primed drywall: 300–350
Textured or porous interior wall: 250–300
Smooth wood / trim (enamel): 350–400; bare or rough wood: 200–300
Smooth lap or vinyl siding: 300–400; stucco / rough masonry: 150–250; unpainted brick: 100–200
Deck or fence (semi-transparent stain): 200–300; primer: 200–300

Worked example: two ways to under-buy

Take 1,050 sq ft of wall. At the smooth-drywall figure of 350 sq ft/gal and two coats, that is ceil(1,050 × 2 ÷ 350) = 6 gallons. But if that wall is bare, porous drywall — effective coverage nearer 250 — the honest number is ceil(1,050 × 2 ÷ 250) = 9 gallons (or you prime first and keep the 6). Trust the label’s 400 and skip the primer and you buy 6, use 9, and make a store run mid-job. The paint coverage calculator lets you test both figures in seconds.

Coverage also depends on how you apply it

Technique and tools move the number too. A brush and roller lay paint down efficiently and waste little. A sprayer is fast and gives a beautiful finish but loses paint to overspray and mist, so your effective coverage drops — plan on more gallons for a sprayed job, especially outdoors in any breeze. A thick nap roller for texture holds and lays more paint than a smooth-wall roller. And a heavy hand simply wastes paint without improving hide. If you switch from a roller to a sprayer between rooms, do not reuse the same gallons-per-room figure — the sprayer will drink more.

Turning coverage into gallons — and back

Coverage works both directions. Forward: gallons = ceil(area × coats ÷ coverage) tells you what to buy. Backward: area covered = gallons × coverage tells you how far the paint you already have will go — useful for checking whether that half-full pail in the garage can finish a room. Both are one line of arithmetic once you have the right coverage number.

The first coat and the second coat cover differently

A subtlety worth planning for: the two coats of a job rarely cover the same. The first coat does the hard work — it hits a more absorbent, less uniform surface (or the primer), so it spreads a little thinner and covers a bit less than the label figure. The second coat goes over an already-sealed, even film, so it flows further and covers closer to (or above) the rated rate. That is why the quantity formula multiplies the whole area by coats and divides by one coverage number: it averages the two out, and rounding up absorbs the difference. Where it bites is if you buy exactly for one coat “to see how far it goes” and then find the thirsty first coat ate more than expected — you are short before the second coat even starts. Buy for the full job, both coats, from the start.

The planner’s coverage habit

Read the spread rate off the exact can you are buying, then adjust down for texture, porosity and a color change rather than trusting the “up to” headline. Prime porous surfaces so the finish coats spread at their rated rate. Round the gallons up, keep a touch-up can, and your coverage math will match the wall — not the label’s laboratory.

And keep one figure written on the can when you are done: how far a gallon actually went on your walls. Next time you paint a similar surface, that measured number beats any label — it already bakes in your texture, your technique and your tools. A planner’s coverage improves job over job precisely because it is grounded in what happened, not what the lab promised.