Paint Calculator

Estimate how much paint to buy for a room, allowing for doors, windows, coats and the ceiling.

How to use the Paint Calculator

  1. Enter the room length, width and wall height in feet or meters.
  2. Enter the number of doors, windows and coats.
  3. Adjust the coverage per gallon if your paint can states a different figure.

How paint quantity is calculated

Paint = (wall area − doors − windows) × coats ÷ coverage

Wall area is the room perimeter multiplied by the wall height. The calculator subtracts 20 sq ft (1.9 m²) per door and 15 sq ft (1.4 m²) per window. A typical gallon of interior paint covers about 350–400 sq ft per coat; a liter covers about 10 m².

For a 14 × 12 ft room with 8 ft walls, one door and two windows: (2 × (14 + 12) × 8) − 20 − 30 = 366 sq ft. Two coats at 350 sq ft per gallon need about 2.1 gallons.

Getting a better result

  • Fresh plaster, bare wood and textured walls absorb more paint.
  • A big colour change usually needs a primer or an extra coat.
  • Buy a little extra for touch-ups.

Frequently asked questions

How much paint do I need for a room?

An average 12 × 12 ft bedroom with 8 ft walls needs about 2 gallons (7.5 liters) for two coats on the walls.

How many square feet does a gallon of paint cover?

About 350 to 400 square feet per coat on smooth, primed walls. A liter covers roughly 10 square meters.

Do I need two coats?

Usually yes. Two coats give even colour and better durability, especially over a different colour.

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