How Much Paint Coverage Should You Expect?

What the can's coverage figure represents

Paint manufacturers state an expected coverage rate (commonly in the range of 250-400 square feet per gallon, varying by product) based on testing under fairly controlled, ideal conditions — a smooth, properly-prepared surface with standard application. It's a reasonable planning figure, but it's not a guarantee for every real-world surface.

The figure is per coat. Two coats over 400 ft² of wall means painting 800 ft², which is the most commonly forgotten step in paint estimates.

Coverage and film thickness

Coverage and film thickness are two sides of the same number. One US gallon spread over 1,604 ft² gives a wet film exactly 1 mil (0.001 in) thick, so wet film thickness in mils = 1,604 ÷ coverage in ft² per gallon. At 350 ft² per gallon, the wet film is about 4.6 mils.

Once the water or solvent evaporates, only the solids remain. The dry film thickness is the wet thickness times the paint's volume solids — so a paint with 35% volume solids at 4.6 mils wet dries to about 1.6 mils. That's why stretching paint to beat the label coverage often leaves a thin, patchy finish that needs another coat anyway.

What causes coverage to vary

• Surface texture — a heavily textured wall absorbs more paint per square foot than a smooth one
• Porosity — bare drywall, unprimed wood, or masonry soak up more paint than a previously painted, sealed surface
• Color change — going from a dark existing color to a much lighter new color (or vice versa) often needs an extra coat regardless of the stated coverage rate
• Application method — spraying, rolling and brushing all deposit paint at somewhat different rates and with different overspray/waste characteristics

Worked example: a bedroom

A 12 × 14 ft room with 8 ft ceilings has 2 × (12 + 14) × 8 = 416 ft² of wall. Deduct one 3 × 7 ft door (21 ft²) and two 3 × 5 ft windows (30 ft²) to get 365 ft². Two coats at 350 ft² per gallon need 365 × 2 ÷ 350 = 2.09 gallons — in practice two gallons plus a quart, or three gallons if you want paint left for touch-ups.

The ceiling (12 × 14 = 168 ft²) is a separate job, usually in a flat ceiling paint. Ceilings are often rolled at a lower spread rate than walls, so the Ceiling Paint Calculator defaults to 300 ft² per gallon: two coats need 336 ÷ 300 = 1.12 gallons, or one gallon plus a quart. On a smooth, primed ceiling at the wall rate of 350 ft² per gallon, it would be 0.96 gallons, so one gallon. The Paint Calculator handles the walls using the 350 ft² per gallon default, and the Wall Paint Calculator deducts the doors and windows for you.

Working backwards from the paint you have

Sometimes the question is the reverse: how far will the paint you already own go? The Paint Coverage Calculator multiplies gallons by the spread rate and divides by the number of coats. Two gallons at 350 ft² per gallon covers 700 ft² in one coat, or 350 ft² in two.

Primer, texture and exterior surfaces

New drywall, patched areas, bare wood and masonry generally need a primer or sealer first. Primer has its own spread rate on its label and is estimated as a separate coat. Heavily textured surfaces such as stucco, split-face block and rough-sawn siding can take far more paint than the label figure — check the product data sheet for a rough-surface spread rate, or test a measured area and scale up.

Planning around the uncertainty

Use the can's coverage figure as your starting estimate, but buy from a supplier that allows returns of unopened cans where possible, and consider a small buffer for a textured, porous, or dramatically color-shifted surface rather than cutting the order exactly to the calculated minimum.

When a job needs several cans of a custom color, mix them together in a larger bucket before starting ('boxing') so any small tint differences between cans don't show up as patches on the wall. The guide to calculating paint for a room goes through measuring each surface.

Common mistakes

• Forgetting to multiply by the number of coats.
• Using the label rate on unprimed or textured surfaces.
• Estimating walls and ceiling together when they take different paints.
• Buying the exact minimum and running out on the last wall.