Paint Calculator
Find out how much paint you need for a room — based on wall dimensions, doors, windows, and the number of coats.
With 414 sq ft of paintable wall and 2 coats, you'll need 2.37 gal of paint.
Paint to buy
Results update as you type. Coverage assumes a typical emulsion at ~350 sq ft/gal; check the tin/can label — porous surfaces, dark-to-light color changes, and primer coats all need more paint.
Formula
Wall area is perimeter × height:
2 × (length + width) × height.
Subtract the typical area for each door and window (1.85 m² and 1.4 m² respectively),
multiply by coats, and divide by coverage (~11 m²/L for emulsion, ~350 sq ft/gal for US).
The calculator rounds up to whole tins because partial cans don't sell.
When this calculator helps
Buying paint by gut feel is how you end up making a second trip to the hardware store mid-project, color still wet on the roller. This calculator removes the guesswork: enter your room's length, width and height in feet, tell it how many doors and windows to subtract, pick your number of coats, and it returns the square footage of wall to cover and the number of gallons — and quarts — you should put in the cart.
It fits the jobs Americans actually take on themselves: repainting a bedroom over a weekend, refreshing a rental before a walkthrough, or rolling a bold accent color onto one living-room wall. Because you choose the coats and the calculator leans on a conservative coverage rate, the gallons it gives you are a dependable shopping number rather than the best-case figure printed on the can.
How to read your result
Two numbers carry the result. The paintable area in square feet is your wall surface after doors and windows are subtracted — a typical 13 ft by 16 ft room at 8 ft high gives roughly 460 sq ft of wall before openings. The gallons figure is that area times your number of coats, divided by a coverage rate of about 350 sq ft per gallon.
From there the calculator rounds up to whole cans, mixing gallons and quarts as needed. Round up, never down: a job that pencils out at 1.3 gallons means a gallon plus a quart, not stretching a single can and hoping. Whatever is left over is worth keeping — sealed, latex paint lasts a couple of years and is exactly what you want on hand for nicks and scuffs later.
A worked example
Picture a 13 ft by 16 ft bedroom with 8 ft ceilings. The four walls come to (13 + 16) × 2 × 8 = 464 sq ft. Subtract one door at about 20 sq ft and two windows at roughly 15 sq ft each, and you have around 414 sq ft of paintable wall. For two coats that is 828 sq ft of coverage, which at 350 sq ft per gallon needs about 2.4 gallons. The calculator rounds that to two gallons plus two quarts — comfortably enough, with a little held back for touch-ups.
Common mistakes to avoid
Most paint shortages trace back to a few estimating slips that are easy to sidestep.
- Skipping the second coat — one coat rarely covers evenly, especially over a color change, so set coats to two unless you are repainting the same color.
- Not subtracting big openings — sliding glass doors or a picture window remove far more wall than the standard averages, so adjust or buy an extra quart.
- Ignoring primer on bare drywall or dark walls — new drywall and deep colors soak up paint, and without a primer coat you may need three finish coats instead of two.
- Taking the can's coverage at face value on textured walls — knockdown, orange-peel or unprimed surfaces can use 15–20% more than smooth drywall.
US paint and can-size notes
American wall paint is sold mostly in gallons and quarts, with the gallon (about 3.8 liters) the workhorse size and quarts handy for trim, accent walls and topping off. Coverage claims of 350 to 400 sq ft per gallon assume smooth, primed drywall, so older homes with plaster, heavy texture or unprimed patches will eat into that number — budget more for anything that is not a clean, sealed surface.
Paint-and-primer-in-one products are common and convenient for repaints in similar colors, but they are not a true substitute for a dedicated primer on new drywall, water stains or drastic color shifts — in those cases prime first, then apply your finish coats. Five-gallon buckets exist for whole-house jobs and usually cost less per gallon, but only make sense when the project is large enough to use the paint before it skins over in the pail.
Related calculators
Frequently asked questions
How many sq ft does a gallon of paint cover?▾
Most US wall paint advertises 350–400 sq ft per gallon per coat. The calculator uses 350 sq ft/gal as a conservative default — real-world coverage is often less because of texture, color changes, and DIY brushwork. Always buy a little extra; running out mid-wall is far worse than having half a quart left over.
How many coats do I need?▾
Two coats for most jobs. Three coats (or two over a tinted primer) for: dark over light, light over dark, fresh drywall, or stained surfaces. One-coat paints work in limited circumstances (same color, premium product) but rarely look as good as the marketing claims.
Should I include the ceiling?▾
Not in this calculator — wall area only. For ceilings, calculate length × width separately. Ceiling paint is usually a different product (flat finish, non-drip, low-spatter) and worth buying separately — using wall paint on a ceiling tends to drip and leave roller marks.
What about primer?▾
Primer is a separate purchase and a separate calculation. As a rough rule, primer covers roughly the same area per gallon as the wall paint that goes over it. For new drywall, water-stained walls, or strong color shifts, primer is essential; for repaints in similar colors over good substrate, you can usually skip it.
Is one gallon enough for a small bedroom?▾
Usually yes for a single coat in a typical 12×12 ft bedroom (~432 sq ft of wall after deductions, well under a single gallon's 350 sq ft). For two coats in that room, plan on about 1 gallon plus a quart, or just two 1-gallon cans.
How much extra should I buy for waste?▾
The calculator is already conservative on coverage. For unusually textured walls, popcorn ceilings (don't paint these — they often need replacement), or aggressive color changes, add ~15% on top of the calculated quantity. Sealed leftover paint stores ~2 years and is invaluable for touch-ups.