How much does a gallon of paint cover?
Interior wall paints commonly publish about 350–400 square feet per US gallon for one coat on a smooth, sealed, previously painted wall — roughly 8.5–10 square metres per litre. That is the number most calculators quietly assume. It is a reasonable starting point and a poor substitute for the rate printed on the product you are actually buying.
Two things move the answer more than anything else: the coat count, which divides the coverage, and the surface, which decides how much of the first coat the wall keeps. Everything below is about getting those two right.
Wall covered at 2 coats
200 sq ft
1 US gal × 400 sq ft/US gal = 400 sq ft of single-coat capacity. Divided across 2 coats, that finishes 200 sq ft of wall.
This is a theoretical figure at the manufacturer's stated rate. Porous, textured, patched, or previously unpainted surfaces absorb more, and a large colour change usually needs an extra coat rather than an extra container.
Work out containers for your wallWhy the label rate is the real answer
Five things that move coverage.
A published spread rate is measured under stated conditions on a stated substrate. Every one of these factors moves the real-world figure, which is why a takeoff that hard-codes 400 square feet per gallon will be wrong for a large share of actual walls.
| Factor | Effect | What to do about it |
|---|---|---|
| Surface texture | Reduces coverage | A textured or heavily orange-peel wall has more actual surface area than its measured dimensions suggest, so the same tin covers fewer measured square feet. |
| Porosity | Reduces coverage | Bare plaster, new filler, and fresh drywall absorb the first coat. This is what a primer or mist coat is for — it stops the topcoat disappearing into the substrate. |
| Colour change | Adds a coat, not a container | Going dark over light, or light over dark, is a coat-count problem rather than a spread-rate problem. A tinted primer usually costs less than a third topcoat. |
| Application method | Varies | Spraying loses material to overspray; rollers hold paint in the sleeve. Manufacturers usually publish their rate for brush and roller application. |
| Product line | Varies by product | Rates differ between a trade emulsion, a premium interior line, and a stain-blocking product from the same brand. Use the sheet for the exact product, not the brand. |
Worked example
A 12 × 12 room, start to purchase.
This is the arithmetic behind the most common version of the question. Nothing here is specific to a brand — swap in your own spread rate and the same steps hold.
Run this with your own measurementsStep 1
Perimeter
2 × (12 ft + 12 ft) = 48 ft of wall to go around.
Step 2
Gross wall area
48 ft × 8 ft ceiling height = 384 sq ft.
Step 3
Subtract openings
One 3 × 7 ft door and two 3 × 4 ft windows = 45 sq ft, leaving 339 sq ft.
Step 4
Apply coats
339 sq ft × 2 coats = 678 sq ft of coating to deliver.
Step 5
Divide by the spread rate
678 ÷ 400 sq ft per gallon = 1.70 gallons of theoretical volume.
Step 6
Round to what you can buy
Two 1-gallon containers, leaving about 0.3 gallons spare for touch-ups.
Where to find your product's rate
Every manufacturer publishes a spread rate on the tin and, in more detail, in the product's technical data sheet. That sheet also states the substrate and film thickness the rate assumes, the recommended coat count, and the recoat time — all of which change the quantity you need. If you cannot find it on the label, search the product name plus “technical data sheet” on the manufacturer's own site rather than a retailer listing.
Read how WallVive separates published product facts from arithmetic and from planning judgements on the methodology page.
Paint coverage questions
Common versions of the coverage question, answered with the arithmetic rather than a single universal number.