How it works
Paint is sold by coverage: one US gallon covers about 350 square feet in one coat, and one litre covers about 10 square metres. Multiply the wall area by the number of coats, divide by the coverage, and you have the paint needed.
The calculator rounds the result up and shows both gallons and litres. Buy a little extra — running out mid-wall leaves a visible join, and a spare tin covers touch-ups later.
Formula
Paintable area = wall length × wall height × number of walls × number of coats. Paint needed = area ÷ 350 sq ft per gallon (about 10 sq m per litre).
What each input means
- Wall length: The length of one wall, in feet.
- Wall height: The height of the wall, in feet.
- Wall length: The length of one wall, in metres.
- Wall height: The height of the wall, in metres.
- Number of walls: How many walls of this size you are painting.
- Number of coats: Two coats is the standard for a lasting finish.
Worked example: 12 ft × 8 ft walls, 4 walls, 2 coats
- One wall: 12 × 8 = 96 sq ft
- Four walls, two coats: 96 × 4 × 2 = 768 sq ft
- Paint needed: 768 ÷ 350 = 2.19 gallons (about 8.3 litres)
- Buy 3 gallons — rounding up covers touch-ups and guarantees the colour matches.
Frequently asked questions
How much does one gallon cover?
About 350 square feet in one coat on a smooth wall. Rough or unpainted surfaces absorb more — allow 300 square feet per gallon for bare plaster or new drywall.
Do I need to subtract doors and windows?
For a rough estimate, no — the extra paint covers them as waste and touch-ups. For a tight budget, subtract about 15 sq ft per door and 10 sq ft per window.
How many coats do I need?
Two coats is the standard for a lasting finish. One coat is enough only when repainting the same colour on a sound surface.
Should I buy extra?
Yes — round up to the next whole gallon. Paint from the same batch matches perfectly, and a spare tin is useful for touch-ups.