Paint Coverage Calculator

How to use the Paint Coverage Calculator

Start by measuring every wall you plan to paint — multiply each wall's length by its height and add the numbers together. That total goes in the Wall area field. Next, count the doors and windows inside that area; the calculator subtracts a standard 20 sq ft for each door and 15 sq ft for each window (1.86 m² and 1.39 m² respectively). Pick your number of coats — two is the safe default for any color change. Finally, check the back of your paint can for the coverage rate: most smooth-wall interior paints get about 350 sq ft per gallon, or 10 m² per liter. Set that number and the result updates as you type.

What is paint coverage and how is it calculated?

Paint coverage is the area a given volume of paint will cover at the manufacturer's recommended thickness. It varies by paint type, surface porosity and color — a flat ceiling paint over a primed surface might stretch to 400 sq ft per gallon, while a deep-pigment paint on raw drywall covers 250. The calculator multiplies your net paintable area (wall area minus doors and windows) by the number of coats, then divides by the coverage rate:

paint = (wall_area − doors × 20 sq ft − windows × 15 sq ft) × coats ÷ coverage

Rounding up to the next can is a habit worth keeping — running short mid-room means a second trip and a paint batch that often doesn't match. A 5–10% buffer is also a good idea so you have color-matched touch-up paint a year from now.

Examples

• Small bedroom (10 × 12 ft): ~400 sq ft of wall, one door, one window, two coats at 350 sq ft/gal — needs about 2.1 gallons. Buy two 1-gallon cans plus a quart for safety.
• Open living room (16 × 20 ft): ~720 sq ft, two doors, three windows, two coats at 350 sq ft/gal — needs about 3.8 gallons. Buy four 1-gallon cans; the extra is cheap insurance and matches for touch-ups later.
• Powder room (4 × 6 ft): ~160 sq ft, one door, no windows, two coats at 300 sq ft/gal (a glossier finish covers less) — needs about 0.9 gallons. A single gallon handles the room and the matching trim.

FAQ

How much paint do I need for one room?

A typical 10 × 12 ft bedroom (~400 sq ft of wall) needs about 1 to 1.25 gallons for two coats of standard interior paint after subtracting one door and one window. Use the calculator for an exact figure.

How do I measure my wall area?

For each wall, multiply length by height. Add the walls together. Skip the ceiling unless you plan to paint it too. Don't subtract windows and doors by hand — let the calculator do it.

One coat or two coats?

Two coats is the default for almost any color change. One coat is only safe as a touch-up over the same color on a clean, primed surface.

What if I am painting over a dark color?

Plan on a primer coat plus two color coats. Dark surfaces also absorb more paint per square foot — drop the coverage rate by 15–20% in the calculator if the can doesn't specify one.

Should I round up?

Yes. Always round up to the next can and buy 5–10% extra for touch-ups months from now. Mixing a second can in the same batch later rarely matches.

Why does coverage vary so much by paint?

Coverage depends on the binder, opacity and finish. Flat paints lay down thinner than semi-gloss; some "one-coat" products are thicker by design. The number on the back of your can is always more reliable than a generic estimate.