How Many Square Feet Does a Gallon of Paint Cover?
Worked scenarios are illustrative composites. Our editorial pen name and method.
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“How many square feet does a gallon cover?” is the question every paint estimate rests on, and it does not have one answer. It has a range, and the spread inside that range is wide enough to change how many cans you carry to the register. Anyone who gives you a single confident number is quietly hiding the three things that actually move it: the product, the surface, and the color. Here is how to pin it down for your job instead of borrowing someone else’s rule.
The honest number is a range
Sherwin-Williams gives roughly 350–400 square feet per gallon as general planning guidance, and warns that product, surface texture, porosity, application and condition all affect the real result. That range is a fine starting point — but treat the label or technical data sheet for the paint you’re actually buying as the truth, because it overrides any site-wide default:
Why the range is so wide
The same gallon behaves very differently depending on where it lands:
- Texture and porosity. Smooth, sealed drywall lets a gallon stretch to the top of the range. Rough, porous, or freshly patched surfaces drink it and pull you toward the bottom — or below it.
- Color and hiding. A drastic color change may need an extra coat, which is really a coverage problem in disguise: the same paint effectively “covers” less area per gallon because you’re applying more of it.
- Application. Roller nap, spray versus brush, and how heavily it’s laid on all move the number.
Watch the range turn into different purchases
Take a measured 391 sq ft of wall, two coats, and see what the spread rate does:
| Spread rate | Exact gallons | Package plan |
|---|---|---|
| 400 sq ft/gal | 1.96 | 2 gal |
| 350 sq ft/gal | 2.23 | 2 gal + 1 qt |
| 300 sq ft/gal | 2.61 | 2 gal + 3 qt |
| 250 sq ft/gal | 3.13 | 3 gal + 1 qt |
Same wall, same two coats — and the honest answer swings from two gallons to more than three purely on coverage. This is exactly why “a gallon does 400 square feet” is a risky thing to build a shopping list on. If your product’s data sheet gives a range, buy off the cautious end unless a test area proves the paint goes further.
Measure openings; don’t apply shortcuts as standards
Gross wall area is perimeter × height. Then subtract the measured area of doors, windows and other surfaces you won’t paint — not a “standard” deduction per opening. Ceiling area is length × width, minus a large skylight if it materially changes the order. Trim is its own measured face area with its own spread rate, because the trim product may differ from the wall paint.
Coverage is not hiding, and paint coverage is not primer coverage
Two separations save a lot of second trips. First, a spread rate tells you area per volume — it does not promise one coat will hide a strong color, seal a porous wall, or block a stain; decide primer and coat count from the coating system, then apply the rate. Second, never infer primer coverage from the paint’s — primer is a different product with its own (often lower) rate, and it gets its own line.
Safety lives outside the coverage equation
A coverage chart cannot tell you a surface is safe to disturb. Don’t sand or scrape suspect old ceiling or wall material on the strength of a paint estimate — the EPA notes that visual inspection can’t confirm asbestos and recommends qualified testing when suspect material is damaged or a renovation will disturb it:
A defensible purchase workflow
- Measure the surfaces and the large openings.
- Read the selected product’s spread rate and required coats.
- Run low/middle/high coverage cases if the label gives a range.
- Convert exact gallons to the package sizes actually sold for that product.
- Enter gallon and quart prices separately — package pricing isn’t proportional.
- Keep the receipt and confirm return rules before counting on unopened-can returns.
Why the label range outranks a universal number
Coverage is a genuine variable, not a fixed spec — which is why every serious manufacturer publishes a range and a “your results may vary” note. Use the arithmetic to plan and a test area to confirm, and read the exact product’s data for anything you’re about to buy in quantity.
The paint calculator exposes separate wall, ceiling, primer and trim coverage inputs instead of hiding them in fixed ratios, so you can run those sensitivity cases directly. These are general-information estimates, not professional advice.