Paint Calculator: How Much Paint Do I Need?

How many gallons of paint by room size

The chart below uses the same formula and assumptions as the calculator: 8 ft walls, one door, two windows, two coats, and 350 sq ft per gallon. Use it for a quick sanity check before you head to the store.

Notice the rows that land just over a whole number, such as 2.1 gallons. Sherwin-Williams estimates a quart covers about 100 sq ft, so when the extra is small, a gallon count plus one quart may be enough instead of another full gallon.

Gallons of paint by room size with 8 ft or 9 ft walls

14 to 15 percent more paint for 9 ft walls than for 8 ft walls in the same room: every wall grows by 1 ft while the doors and windows stay the same size, so the paintable area grows more than the 12.5 percent of the bare wall. The chart uses the calculator's one door, two windows and 350 sq ft per gallon. One coat is for a fresh coat of the same color over sound paint; the last column adds the ceiling, painted with the same two coats.

The calculator rounds the same numbers to one decimal. Where a row lands just over a whole number, such as the 12 x 12 ft room with 9 ft walls and the ceiling at 3.01 gallons, it says buy 4, but 3 gallons and a quart cover it. Rooms with more doors and windows, or textured walls, need their own numbers: enter them in the calculator above.

Paint coverage per gallon by product

The coverage number is the biggest lever in the estimate, and it varies by product and surface. Here is what manufacturers and PaintCare publish:

Our calculator defaults to 350 sq ft per gallon because it sits in the middle of these ranges. If your label says 400 and your walls are smooth and already painted, type 400. If you are painting textured plaster or bare drywall, go lower.

Paint coverage per gallon by surface: smooth, textured, new drywall

Up to 400 sq ft per gallon on smooth surfaces and 200 to 300 sq ft on rough ones, says PPG's technical data sheet for its Painter's Friend interior wall paint, so a textured wall can take up to twice the paint of a smooth one. Type the rate for your surface into the calculator's coverage box; the last column is the calculator's default 12 x 10 ft room, with 302 sq ft of walls.

So new drywall in that room takes 1 gallon of drywall primer plus 2 gallons of paint. Sherwin-Williams gives 200 to 300 sq ft per gallon for primer in general, and a drywall primer's label can list more, as Benjamin Moore's does, so read the can. For the primer coat, run the calculator with 1 coat and the primer's coverage.

How far a quart, a gallon, and a 5-gallon bucket go

Coverage grows with the amount of paint and divides by the number of coats. The gallon rows use the calculator's 350 sq ft per gallon, with PaintCare's 300 to 400 sq ft range in parentheses; the quart is Sherwin-Williams' estimate.

Put the other way, every 100 sq ft of wall takes about 0.29 gallon per coat at 350 sq ft per gallon, or 0.57 gallon for two coats.

Gallons of paint by square feet

100 to 3,000 sq ft, from one wall to a whole house: find your paintable area, after doors and windows, and read across. Every cell is gallons. The column heads are sq ft per gallon: 400 for smooth, primed surfaces (PPG, Glidden), 350 when you do not know the product (PaintCare), 250 for the low end of Behr's range, and 200 for rough surfaces (PPG).

A gallon is 4 quarts and a bucket is 5 gallons, so the 11.43 gallons that 2,000 sq ft takes for two coats at 350 is two 5-gallon buckets plus 2 gallons. For a house exterior, Behr measures the perimeter times the height from the foundation to the roofline, adds width x height / 2 for each gable, subtracts about 20 sq ft per door and 15 per window, and adds 1 gallon of trim and gutter paint for every 8 gallons of body paint. PPG's data sheet for its Acri-Shield exterior paint lists up to 400 sq ft per gallon on smooth surfaces and 200 to 250 on rough ones.

What changes how much paint you need

Wall texture and porosity

Smooth, sealed walls let paint go the farthest. PaintCare notes that rough textures can take up to 50 percent more paint. Behr likewise lists porous, rough, and textured surfaces as ones that take more paint. On heavily textured walls or bare masonry, lower the coverage number before you calculate.

Color changes

Going from a similar shade to another is the easy case. Dark-to-light and light-to-dark changes can take three or even four coats, and PaintCare points out that some vivid colors, especially reds, oranges, and purples, can take more. A tinted primer as the first coat often cuts the number of finish coats; PaintCare specifically suggests a gray primer under red.

New or unpainted drywall

Bare drywall is both porous and previously unpainted, two of the conditions Behr flags as needing more paint. Prime it first, and budget primer at its own coverage rate. Sherwin-Williams puts primer at about 200 to 300 sq ft per gallon, so a room that needs 302 sq ft of walls will need roughly one to one and a half gallons of primer on top of the paint. Still hanging the drywall? The drywall calculator counts the sheets.

Trim, doors, and ceilings

Trim is often painted in a different sheen or color, so estimate it separately. Behr suggests multiplying the total length of your trim by 0.5 ft to get its approximate square footage. If you need the length, our baseboard calculator gives you the linear feet for a room. Papering a wall instead? The wallpaper calculator counts the rolls.

1 quart covers one door or one room's baseboard with two coats. The chart uses Sherwin-Williams' 100 sq ft per quart when two coats come to 100 sq ft or less and 350 sq ft per gallon above that, a 36 x 80 in door (20 sq ft a side), and Behr's 0.5 ft for trim:

The 41 ft is the baseboard calculator's default 12 x 10 ft room less one doorway of about 3 ft. To paint a ceiling with the walls, tick "Paint the ceiling too" in the paint calculator; for a separate ceiling paint, use the ceiling rows.

Application method

Sherwin-Williams notes that paint requirements vary with the application method as well as the surface type and condition. If you plan to spray, check the product data sheet for its application notes and round your estimate up rather than down.

Common mistakes to avoid

• Using floor area instead of wall area. A 12 x 10 room has 120 sq ft of floor but over 300 sq ft of wall. Multiply the perimeter by the height.
• Forgetting the second coat. A single-coat estimate is half the paint you will actually use on most jobs.
• Taking the best-case coverage number. The top of a label's range assumes ideal surfaces. Use the low end on rough, patched, or unpainted walls.
• Measuring to the top of the baseboard. Measure floor to ceiling. The small overestimate from the baseboard strip is a buffer, not a problem.
• Ignoring big openings. A sliding patio door or a bank of windows removes far more than 20 or 15 sq ft. Count them as multiple doors or windows.
• Buying exactly the decimal. Round up. A little left in the can is what you will use for touch-ups later, and PaintCare suggests leftover paint can also serve as a base coat on another project.