How Much Paint Do I Need? A Simple Room Method

Buying too little paint means a second trip and possibly a slightly different batch color. Buying too much wastes money. A few measurements get you close.

Step 1: Measure the wall area

Measure each wall's width and the room's height, then multiply. For a rectangular room you can use the perimeter instead:

A 4 m × 3.5 m room with 2.4 m ceilings has (4 + 3.5) × 2 × 2.4 = 36 m² of wall.

Step 2: Subtract doors and windows

Use rough sizes if you don't want to measure each one: a standard interior door is roughly 2 m² (about 20 sq ft) and a typical window about 1.5 m² (about 15 sq ft). Take off the big openings and ignore small ones like light switches.

Step 3: Allow for coats and coverage

Check the tin for coverage. Many interior paints cover around 10 m² per liter per coat (about 400 sq ft per US gallon). Plan on two coats, especially when covering a darker color.

Example: 36 m² minus one door (2 m²) and one window (1.5 m²) leaves 32.5 m². Two coats makes 65 m². At 10 m² per liter you need about 6.5 liters, for example a 5 L tin plus a 2.5 L tin.

Step 4: Add a margin

Rough or porous surfaces such as new plaster, bare wood or textured walls soak up more paint. Add about 10% extra, and keep any leftover, labeled with the room and date, for touch-ups.

Ceilings and trim

The ceiling area is simply length × width (4 × 3.5 = 14 m² in the example). Trim and doors usually take a different paint, so estimate them separately.