Paint Calculator

Work out how much paint to buy for a room. Enter the total length of the walls, the height, the number of doors and windows and how many coats you will apply.

How to use the Paint Calculator

Measure and add up the length of all walls (the room’s perimeter).
Enter the wall height, doors, windows and number of coats.
Adjust the coverage per gallon if your paint can lists a different figure.

How it works

Paintable area = perimeter × height − doors − windows (about 20 sq ft per door and 15 sq ft per window). Gallons = area × coats ÷ coverage. Most interior paints cover about 350–400 sq ft per gallon on smooth, primed walls; textured or porous surfaces need more.

Paint for a room with 8 ft walls, 1 door, 2 windows, 2 coats

Room	Wall area	Gallons
10 × 10 ft	270 sq ft	1.5
12 × 12 ft	334 sq ft	1.9
12 × 14 ft	366 sq ft	2.1
14 × 16 ft	430 sq ft	2.5
16 × 20 ft	526 sq ft	3

Frequently asked questions

How much paint for a 12×12 room?

About 2 gallons for two coats on 8 ft walls (around 334 sq ft of wall after doors and windows).

How much does a gallon of paint cover?

About 350–400 sq ft per coat.

Do I need two coats of paint?

Usually yes, especially when changing colour or painting new drywall.