How Much Paint Do You Need for a Room?

Measure the length of each wall and the height from floor to ceiling. The quickest method is to add all the wall lengths together (the perimeter) and multiply by the height:

Wall area = Perimeter × Height

A 14 × 12 ft room has a perimeter of 14 + 12 + 14 + 12 = 52 ft. With 8 ft ceilings, the walls total 52 × 8 = 416 sq ft.

Measure each door and window and subtract its area. A standard interior door of about 3 × 7 ft is roughly 21 sq ft; a 3 × 4 ft window is 12 sq ft. Small items such as switch plates and vents are not worth subtracting.

With one door and two windows: 416 − 21 − 24 = 371 sq ft of paintable wall.

The can or data sheet states how much area one unit covers in one coat, for example 350 sq ft per gallon, or 10 m² per litre. Figures vary by product, and real-world coverage is lower on:

• new drywall or bare plaster, which absorb paint (a primer or mist coat is often recommended);
• textured or rough surfaces, which have more surface area;
• dark-to-light colour changes, which may need an extra coat.

Paint = Paintable area × Coats ÷ Coverage

For 371 sq ft, two coats at 350 sq ft per gallon: 371 × 2 ÷ 350 = 2.12 gallons. That means buying three one-gallon cans, or two gallons plus one quart (0.25 gal) if that leaves enough margin for your surface.

In metric: a room with 36 m² of paintable wall, two coats at 10 m²/L, needs 7.2 litres. You could buy one 5 L and one 2.5 L tin.

• Ceilings: area = room length × width. The 14 × 12 ft room has a 168 sq ft ceiling. Ceiling paint is usually a separate product, so calculate it separately.
• Trim and doors: usually painted in a different finish. Estimate the area as trim length × trim width (plus both faces of each door) and use the coverage on that product’s can.

• Buy all the paint for one room at the same time, and mix cans together before starting to avoid colour differences.
• In the US, paint is sold in quarts, gallons and 5-gallon buckets; in the UK and Australia, in litres (commonly 1, 2.5, 5 and 10 L); in Canada, often 3.78 L cans.
• Keep a small, labelled amount for touch-ups.

The paint calculator measures walls by width and count or by perimeter, subtracts doors and windows, and rounds up to your chosen can size. Hanging new drywall first? Use the drywall calculator. To total floor areas, see the square footage calculator.