The number on the paint can says one gallon covers 350 to 400 square feet. That number is true, and it is also the reason so many people run out mid-wall. The catch is that it describes one coat, on a smooth, already-painted surface, under ideal conditions. Real rooms are rarely that generous. Here is how to estimate paint you can actually trust.
How far a gallon really goes
A gallon covers 350 to 400 square feet in a single coat on a smooth, sealed surface. Use 350 as your working number, because it builds in a small margin and most walls are not perfectly smooth.
But you rarely paint just one coat. You need two coats when you are:
- Painting new or bare drywall
- Going from a dark color to a lighter one
- Using a color with weak coverage (many reds and yellows)
- Painting over a patchy or stained surface
So for most real projects, plan on 175 square feet of coverage per gallon, which is 350 divided by two coats. This one adjustment is what separates an accurate estimate from a second trip to the store.
The step-by-step method
1. Measure the wall area. For each wall, multiply width by height, then add the walls together. For a 12 by 14 foot room with 8 foot ceilings:
- Two 12 foot walls: 2 × (12 × 8) = 192 sq ft
- Two 14 foot walls: 2 × (14 × 8) = 224 sq ft
- Total wall area: 416 sq ft
2. Subtract doors and windows. Use 20 square feet per door and 15 per window. With one door and two windows: 416 − 20 − 30 = 366 sq ft.
3. Divide by coverage. For two coats at 175 sq ft per gallon: 366 ÷ 175 = 2.1 gallons. Round up to buy 3 gallons, or 2 gallons plus a quart if you want to trim it close.
Do not forget the ceiling
Ceilings are easy to overlook. A ceiling is just length times width. Our 12 by 14 room has a 168 square foot ceiling, which needs its own paint (usually a flat white ceiling paint, not wall paint). That is about a gallon on its own for two coats.
Primer changes the math
Primer is not optional on bare drywall. New drywall soaks up paint unevenly because the paper facing and the joint compound absorb at different rates. A coat of primer seals the surface so your finish coats go on evenly and cover in two coats instead of three.
If you skip primer on new drywall, you will often need a third coat of finish paint, which usually costs more than just buying the primer. If you are painting a freshly hung room, size the drywall itself with our drywall calculator so the whole material list lines up.
Texture eats paint
The 350 to 400 figure assumes a smooth wall. Texture increases the surface area the paint has to cover:
- Light orange peel: add about 10 percent
- Knockdown texture: add about 15 percent
- Heavy or popcorn texture: add 20 percent or more
Rough exterior surfaces like stucco and brick are even hungrier and can cut coverage nearly in half.
Quick reference
| Project | Coverage to plan for |
|---|---|
| Smooth wall, repaint, 1 coat | 350 sq ft/gal |
| New drywall or color change, 2 coats | 175 sq ft/gal |
| Textured wall, 2 coats | 150 sq ft/gal |
| Stucco or brick, 2 coats | 120 sq ft/gal |
Let the calculator do it
The math is simple but easy to fumble across four walls, a ceiling, and door and window deductions. Our paint calculator handles the full room, applies the coat count you choose, and returns gallons plus a cost estimate. For a single room with trim and ceiling, the room paint calculator breaks it out surface by surface.