How Much Does a Gallon of Paint Cover?

Buying paint is a guessing game if you don't know the math. Buy too little, and you are making a second trip to the hardware store with wet brushes waiting. Buy too much, and you are stuck storing half-full cans in your garage for years.

To get it right the first time, you need to understand standard paint coverage.

The Standard Coverage Rule

As a general rule of thumb, one gallon of interior wall paint covers about 350 to 400 square feet in a single coat. However, this number changes based on a few factors.

Interior Paint Coverage

Walls (Smooth): 350 - 400 sq ft per gallon.
Ceilings: 350 sq ft per gallon (ceiling paint is often thicker to prevent drips).
Trim & Doors: 350 sq ft per gallon. Since trim is narrow, you will likely only need a quart, which covers about 100 sq ft.
Primer: 250 - 300 sq ft per gallon (primer is porous and absorbs faster).

Exterior Paint Coverage

Exterior surfaces are usually rougher (like stucco, brick, or wood siding), which means they soak up more paint. Expect one gallon of exterior paint to cover 250 to 350 square feet.

Factors That Reduce Coverage

You will get less coverage (meaning you need more paint) if:

You are painting bare drywall or wood: These absorb a massive amount of paint on the first coat.
The walls are textured: A "popcorn" ceiling or rough stucco has more surface area than a flat wall.
You are changing colors dramatically: Going from dark blue to white will require multiple coats.
You are using cheap paint: Budget paints have less pigment and require extra coats to look solid.

How to Calculate Exactly How Much You Need

To figure out how many gallons you need for a specific room:

Measure the length and width of the room. Multiply them to get floor area.
Multiply the perimeter of the room by the wall height to get the total wall area.
Subtract 20 sq ft for every door, and 15 sq ft for every window.
Divide that number by 350.
Multiply by 2 (because you almost always need two coats).

Skip the manual math and use our free Paint Calculator. It does all the square footage math for you and tells you exactly how many gallons to buy.