Last updated: 2026-05-16

Getting the Right Amount of Paint

Planning a paint job goes wrong in one of two ways: you run out mid-wall and can't match the colour, or you buy so much that six half-used cans clutter the garage for a decade. This calculator finds the sweet spot — the minimum number of whole cans that will complete the job.

How It Works

Enter your wall area, the coverage rate from the paint tin, the number of coats, the can size, and the price per can. The calculator runs four steps:

where $A$ is wall area (m²), $n$ is number of coats, $c$ is coverage rate (m²/L), $s$ is can size (L), and $p$ is price per can. The ceiling function $\lceil \cdot \rceil$ rounds up to the next whole can.where $A$ is wall area (sq ft), $n$ is number of coats, $c$ is coverage rate (sq ft/gal), $s$ is can size (gal), and $p$ is price per can. The ceiling function $\lceil \cdot \rceil$ rounds up to the next whole can.

Coverage Rates by Paint Type

Different paints spread at different rates, and the surface condition matters as much as the product:

The spreading rate is printed on every tin, usually labelled "coverage" or "spreading rate". If your tin gives sq ft/gal instead of m²/L, multiply by 0.0245 to convert.

Common Can Sizes

Retail sizes are fairly standardised: 1 L (touch-up), 2.5 L (small room), 4 L or 5 L (standard room), 10 L (large project), and 18.9 L (5 US gallons, trade use). Choosing a larger can size usually reduces leftover waste.