How Much Does a Gallon of Paint Cover?

A gallon of architectural paint covers 350 to 400 square feet in one coat. That is the figure commonly printed on the can, and it is the right place to start.

It is also a best case. It assumes a smooth, sealed, primed surface, one coat, applied with a roller, at the film thickness the manufacturer tested. Change any of those and the real rate falls, on some surfaces by more than half.

Before you know anything about your walls, work on 350 sq ft per gallon for a previously painted interior wall in sound condition, and 250 to 300 for anything porous, textured, or unprimed. The rest of this guide is the detail behind those two figures, one variable at a time.

Where the label figure comes from

Coverage rates are not established by painting a wall and seeing how far the can goes. They are calculated, which is part of why they are optimistic.

A gallon spread to a dry film one mil thick, a thousandth of an inch, would cover 1,604 sq ft if the paint were pure solids. It is not: between a quarter and a half of what is in the can is water or solvent that leaves as it dries, and what stays is the volume solids.

1,604 x volume solids ÷ dry film thickness in mils = square feet per gallon

At 38 percent volume solids and a 1.5 mil dry film, that is 1,604 x 0.38 ÷ 1.5 = 406 sq ft per gallon, which is where a label claim of “up to 400” comes from. It is a theoretical spread rate, at a stated film thickness, on a surface that absorbs nothing. Every correction below is a reason your wall takes more.

Surface porosity: the largest single correction

Porosity is what separates 400 sq ft per gallon from 100. An unsealed surface pulls liquid out of the first coat before the film can level, so part of the gallon ends up inside the wall rather than on it.

Typical first-coat rates, all of them ranges because product and substrate both vary:

• Previously painted, sound, smooth drywall or plaster: 350–400 sq ft/gal. This is the label condition, and you will get close to it.
• New, unprimed drywall: 200–300 sq ft/gal. The paper face and the joint compound over the seams absorb at different rates, which is why an unprimed wall painted directly often shows its seams. Area for new work comes off the same take-off as the board itself, which the drywall calculator produces.
• Bare planed softwood: 250–350 sq ft/gal. End grain and knots take far more than the face does.
• Weathered or rough-sawn wood: 150–250 sq ft/gal. Wood that has spent a few seasons outside is opened up and fibrous, and it drinks. Exterior areas come from the siding calculator and, for rails and decking, the deck calculator.
• Smooth poured concrete: 200–300 sq ft/gal.
• Concrete block: 75–150 sq ft/gal on the first coat. Open-face CMU has voids that no amount of rolling will fill with finish paint. Block filler exists for exactly this and is commonly labelled at 75 to 125 sq ft per gallon, roughly a quarter of what wall paint claims. The concrete block calculator gives the wall area from a block count.

On a porous substrate the second coat goes much further than the first, because the first did the sealing. Correct the first coat hard and the second barely at all.

Texture: more wall than you measured

A tape measure gives you flat area. Paint has to cover actual surface, and texture makes those two different numbers.

Light orange peel adds roughly 5 to 10 percent. Knockdown and skip trowel add 10 to 20 percent. Heavy texture, popcorn ceilings, stucco and split-face block add 25 to 50 percent, and on the worst of them the effective rate is close to half the label figure.

Texture compounds with porosity rather than replacing it: stucco is both rough and absorbent, and a popcorn ceiling is the most reliable way to run out of paint mid-room.

Primer: it repairs the topcoat’s rate, and has its own

Primer does two things to your numbers. It seals the substrate, which brings the topcoat back toward its label rate, and it is a purchase with a coverage rate of its own.

Primers are commonly labelled anywhere between 200 and 400 sq ft per gallon, a wider spread than finish paint because the category is wider: a thin drywall sealer and a high-build masonry filler are both primers. Read the can rather than assuming it matches the topcoat.

The economics almost always favour priming a porous wall. A gallon of primer at 300 sq ft plus two gallons of topcoat at 350 covers more reliably, and usually more cheaply, than three gallons of topcoat fighting an absorbent surface.

Colour: deep bases are built to cover badly

Paint is sold in tinting bases, and the base matters more than the colour name. The deeper the base, the less white pigment it holds, because the colourant needs somewhere to go. A light base may take 2 to 4 ounces of colourant per gallon; a deep or accent base commonly takes 8 to 12 or more. The displaced white pigment is precisely what provides hide, so a deep base covers poorly by formulation rather than by defect.

The label on a deep base still says 350 to 400 sq ft per gallon, and per coat that may be true. What changes is the number of coats, and so the rate across the whole job. A colour needing three coats instead of two delivers about 117 sq ft of finished wall per gallon rather than 175.

The answer is not a third topcoat but a tinted primer: a cheaper product tinted toward the finish colour so the topcoat starts close to its own shade. Many manufacturers publish a grey scale, numbered roughly one to eight, saying which grey primer belongs under a given colour, and following it is often the difference between two topcoats and four.

Reds and yellows are the notorious cases, and the reason is chemistry rather than a defective tin. Clean, saturated shades in those ranges depend on organic pigments, which transmit light instead of scattering it the way the titanium dioxide in a white base does. Hiding power is the property being traded away for the chroma, so a deep red over a pale wall behaves exactly as designed when it takes a fourth coat.

Sheen: the same paint applied with different care

Sheen barely moves the labelled spread rate. Flat, eggshell, satin and semi-gloss from one product line are often labelled inside the same 350 to 400 range. What sheen changes is how much paint the job consumes, which is a different question.

Flat forgives. It scatters light, hides roller laps and minor wall defects, and touches up almost invisibly, so a scuff gets spot-painted rather than recoated. Its weakness is that it marks, and burnishes when cleaned.

Higher sheens reflect, and reflection shows everything: every lap mark, every missed patch, every dent in the board, and every touch-up as an area of different gloss. That forces a different way of working. You keep a wet edge, roll the full height in one pass, and repaint a whole wall later rather than dabbing at it. The result is more paint for the same area, not because the film is thicker but because partial coats stop being an option, and the higher the sheen the more the preparation has to go up too.

Application method: the sprayer costs you paint

The label rate assumes a roller. The other two methods are not close to it.

Method	Effect on consumption	Why
Brush	Slightly more than a roller on flat area, far more on profiles	A loaded brush lays heavy, and trim has more surface than it measures
Roller	The baseline the label assumes	Nap depth sets how much film gets deposited
Airless sprayer	Commonly 20–40% more for the same area	Overspray, bounce-back, and material left in the pump and hose

Nap depth is the part people miss. A 3/8 inch nap is for smooth walls, 1/2 inch for light texture, and 3/4 to 1 1/4 inch for heavy texture and block. A thicker nap holds more paint and lays a heavier film, which is the whole point on a rough surface, but the same wall then consumes noticeably more.

Spraying is a transfer efficiency problem. Not everything leaving the tip lands on the wall: a share atomises, bounces back, or drifts, and airless equipment is the efficient end of spraying yet still loses a meaningful fraction. The machine also holds paint you never get back, since a 50 foot hose and pump contain between a half and a full quart depending on diameter, most of it lost at flush-out.

That is not an argument against spraying, which is fast and reaches profiles a brush cannot. It is an argument for buying above the roller arithmetic when you spray, and for back-rolling a sprayed first coat on porous substrate.

Product grade: what the extra money buys

Two gallons with the same label spread rate can behave very differently, because spread rate is not hide.

The difference is mostly volume solids and pigment quality. Economy lines commonly sit around 25 to 35 percent volume solids, premium lines nearer 35 to 45. Higher solids leaves more film on the wall per coat at the same spreading rate, and better white pigment and resin mean that film hides more. A premium paint does not go further per gallon. It gets there in fewer coats, and a gallon that hides in two beats a budget gallon needing three even at twice the price, because the third coat costs both material and a day.

Turning a corrected rate into cans

Gallons = area ÷ corrected rate x coats.

A 15 by 20 foot room with 9 foot ceilings has a 70 foot perimeter, so 630 sq ft of wall. Take out a door and two windows and call it 580 sq ft. For what to subtract and what to ignore, the paint calculator handles the take-off.

Repaint, sound primed walls, modest colour change. Corrected rate 375 sq ft/gal, two coats: 580 ÷ 375 x 2 = 3.09 gallons. Buy three gallons and a quart.

Same room, new unprimed drywall, deep red. Primer at 300 sq ft/gal, one coat: 1.93 gallons, so two. Topcoat over grey-tinted primer at 350 sq ft/gal, two coats: 3.31 gallons, so three gallons and two quarts. The same room, roughly twice the material.

Then round to what the shop actually sells. Paint comes in quarts, gallons and five gallon pails with nothing in between, so the last container is almost always part used. Three things follow:

• A five gallon pail usually costs less than five separate gallons, commonly 10 to 20 percent less, and comes from a single tint run. If your number lands near five, price the pail first.
• Above two quarts, buy the gallon. A quart covers roughly 85 to 100 sq ft at the label rate, but is commonly priced at 40 to 50 percent of the gallon price while holding a quarter of the paint, so two quarts cost close to a gallon and give you half as much. Quarts are for a single door, a short run of trim, or several colours in small amounts.
• The remnant is not waste. A part-used can labelled with the colour code, base and sheen is your touch-up supply for years. Buying exactly enough is a false economy.

Paint is unusual that way. For most materials the leftover is genuinely waste and the allowance exists to cover cuts and breakage, which is a different calculation with different numbers per trade. The material waste factors guide sets out which is which, and why attic stock is a third thing again.