OnSumoTools

Paint Coverage Calculator

Estimate gallons and cans for any room with doors, windows, coats, texture, and optional ceiling paint.

Walls

Openings

Each standard door counts as 20 sq ft.

Paint specs

Gallons (with waste)

2.29

Cans to buy

3

Estimated cost

$120

Buy 3 x 1-gallon cans

About 9.2 quarts if you buy quart cans instead. Includes 10% waste.

Area breakdown

Total wall area
432 sq ft
Openings deducted
68 sq ft
Net paintable area
364 sq ft
After texture
364 sq ft
After coats
728 sq ft

Wall-by-wall breakdown

WallArea (sq ft)
Wall 1108
Wall 2108
Wall 3108
Wall 4108

Paint amounts are estimates. Check the label on your can for coverage on your surface before you buy.

How does the Paint Coverage Calculator work step by step?

List each wall width and height, subtract doors and windows, then pick coats and surface texture. The calculator adds 10% waste and rounds up to whole one-gallon cans.

What does a typical Paint Coverage Calculator result look like?

A 12 by 12 ft room with 9 ft walls (four walls at 12 x 9 ft), one door, two medium windows, and two smooth coats at 350 sq ft per gallon needs about three one-gallon cans with waste included.

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Frequently asked questions

  • What is standard paint coverage?

    Most latex interior paints cover 350 to 400 square feet per gallon on smooth, previously painted walls. Textured or porous surfaces such as bare drywall, masonry, or heavily orange-peeled walls absorb more paint and typically yield 250 to 300 square feet per gallon. Always check the coverage rate printed on the specific can you plan to use.

  • Should I buy extra paint?

    Yes. Order 10 to 15 percent more than the bare square footage calculation suggests. Paint is manufactured in batches, and a can purchased months later may have a slightly different tint that is noticeable on touch-ups. Store any sealed leftover cans in a temperature-controlled space away from freezing temperatures to keep the paint usable.

  • How many coats do I need?

    Two finish coats are the standard for most repaint jobs over a similar color. Switching from a dark wall to a much lighter color may require three coats to achieve full hide. Bare or patched drywall typically needs a coat of primer first before any finish paint so the topcoats cover evenly and the sheen stays consistent.

  • Does ceiling paint count the same way?

    Turn on the ceiling toggle to add your ceiling square footage and choose a coat count for that surface separately. Flat ceilings often use the same formula as walls. Many painters choose a ceiling-specific flat paint at a lower sheen level to minimize light reflection and hide surface imperfections that would show under a semi-gloss or eggshell finish.

Buy the right amount, once

Short on paint halfway through a wall is a pain, and a mismatched second can is worse. Going the other way leaves you with half-used cans in the garage for years.

Add a row for each wall with its width and height. The calculator finds the total area, takes off doors and windows, and works out the gallons you need for the number of coats you pick.

What goes into the math

A gallon of standard paint covers about 350 to 400 square feet on a smooth wall. Check the label on your can, since it varies by brand. The tool lets you adjust it.

Textured walls soak up more paint, so there's a texture setting that raises the amount. Bare drywall or a big color change often needs a primer coat, or an extra coat of paint.

  • Two coats is the normal plan for a color change
  • Dark colors over light, or the reverse, can need three
  • Ceilings are their own row, usually with flat ceiling paint

A quick example

A bedroom is 12 by 14 feet with 8-foot walls. The wall area is 2 x (12 + 14) x 8, which is 416 square feet. Take off one door at 20 and two windows at 15 each, and you're at 366.

Two coats means 732 square feet of paint. At 350 square feet per gallon, that's just over two gallons. You'd buy three, or two gallons and a quart if you want to save a few dollars.

The ceiling is separate. At 168 square feet, one coat of flat white fits in a single gallon with room left.

Prep matters more than people think

Patch holes, sand rough spots and wipe off dust. Clean greasy spots in kitchens and baths. Paint hides small flaws poorly and large ones not at all.

Use tape on trim and floors, and take it off before the paint fully dries so it doesn't peel the edge. Cut in around the corners first, then roll the open areas while the edge is still wet to avoid lap marks.

A good roller cover makes a bigger difference than an expensive can. Match the nap to the surface. Short nap for smooth walls and longer for textured ones.

Doors, windows and trim

A standard door is roughly 20 square feet and a medium window about 15. Enter the count and the tool subtracts that area. Trim and doors usually get a different finish, like satin or semi-gloss, so treat them as a separate buy.

Round up to the next can, and think about buying a small extra for touch-ups. Keep a splash of the leftover in a labeled jar.

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