Paint Coverage Explained
What "350 square feet per gallon" really means, why real-world coverage varies, and how to read the spread rate on a paint can so your estimate matches what actually happens on the wall.
A gallon of interior latex paint covers about 350 square feet in one coat on a smooth, previously painted wall — premium paints claim up to 400. That number, called the spread rate, drops on porous, rough, or freshly primed surfaces because they absorb more paint. Always plan around the lower end of a can's stated range for a repaint, and lower still for new drywall.
Coverage — sometimes called the spread rate — is the single number that turns square footage into gallons. Every other part of a paint estimate is measurement; coverage is where paint estimates go wrong, because the figure printed on the can is a best case that rarely survives contact with a real wall. This guide explains what the number means and how to use a realistic one.
Want the number without the theory? The paint calculator starts from 350 sq ft per gallon and lets you adjust it for your surface.
What “350 sq ft per gallon” means
Coverage is how many square feet one gallon covers in one coat. The industry rule of thumb for interior latex is about 350 square feet per gallon. Premium paints — thicker, with more solids — advertise up to 400. That’s the range you’ll see quoted on most cans.
So a gallon covers roughly the walls of a small bathroom in a single pass. Since most jobs need two coats, a gallon realistically finishes about 175 sq ft of wall. Keep that in mind when a label boasts “covers up to 400 sq ft” — that’s one thin coat on a perfect surface.
Why real coverage is almost always lower
The spread rate on the can is measured under ideal lab conditions: a smooth, sealed, non-absorbent surface, a full wet film, and a roller loaded just right. Your wall is different in three ways:
- Absorption. Bare drywall, joint compound, raw wood, and masonry pull paint into themselves. More paint soaks in, so less spreads across the surface.
- Texture. A textured or knock-down wall has more actual surface area than its flat footprint suggests — every bump and valley needs coating.
- Application. Rollers, corners, and cut-in lines all lay paint at slightly different thicknesses. Nobody applies a perfectly uniform film.
The result: a paint that claims 400 sq ft might deliver 300 on a smooth repaint and closer to 250 on fresh, unprimed drywall.
Reading the spread rate on the can
Look for a line like “Coverage: 350–400 sq ft per gallon.” Two habits keep you honest:
- Plan around the low end of the stated range for a repaint over a similar color.
- Go below the range entirely for new, rough, or porous surfaces — or prime them first to seal the surface (see How Many Coats of Paint Should You Apply? for when primer is worth it).
If your paint states a coverage figure, type it into the paint calculator — otherwise the default 350 is a safe, conservative starting point.
How coverage changes your gallon count
Coverage is a divisor, so small changes swing the result. Take 730 sq ft of coverage needed (a 12 × 14 room, two coats):
| Coverage rate | Gallons needed | Buy |
|---|---|---|
| 400 sq ft/gal (premium, smooth) | ~1.8 | 2 gallons |
| 350 sq ft/gal (standard) | ~2.1 | 3 gallons |
| 275 sq ft/gal (textured / porous) | ~2.7 | 3 gallons |
| 250 sq ft/gal (new drywall) | ~2.9 | 3 gallons |
The thirstier the surface, the more you buy for the exact same room. That surface effect is big enough to deserve its own guide — see Paint Coverage by Surface.
Putting it together
Coverage is the lever that makes or breaks an estimate. Start from 350 sq ft per gallon, adjust down for texture and porosity, and always round your final gallon count up. For the complete method — area, openings, coats, and coverage in one flow — head back to How Much Paint Do I Need? or let the paint calculator apply the right rate for you.