Paint Coverage Calculator

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:

V = A \times n \div c

N = \lceil V \div s \rceil

C = N \times p

V_{\text{left}} = N \times s - V

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.

Coverage Rates by Paint Type

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

Surface / Product	Typical coverage (m²/L)
Emulsion on primed drywall	10 – 12
Primer on bare drywall	8 – 10
Gloss / semi-gloss trim	10 – 14
Exterior masonry paint	6 – 8
Textured or porous surface	4 – 6

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.

Frequently Asked Questions (FAQ)

Where do I find the coverage rate?

On the back of the paint can or the product datasheet, usually as "spreading rate" or "coverage" in m²/L (metric) or sq ft/gal (imperial). Convert: 1 sq ft/gal ≈ 0.0245 m²/L. If you only have a per-coat figure, use it as-is and set coats = 1.

Why does the calculator default to two coats?

Two coats is the standard for water-based interior emulsion: the first coat seals and equalises the surface, the second delivers the final colour and uniform sheen. Going from a dark colour to a light colour, or painting over bare drywall, may need three.

Should I subtract doors and windows?

For a quick estimate, no — the small over-allocation covers spills, brush loading, and rolls. For a sharp estimate on a large room, subtract any opening over ~1 m². A standard interior door is ~2 m²; a typical window is 1–2 m².

How long does leftover paint keep?

Water-based latex/emulsion stays usable for 2–10 years if the can is well-sealed and stored above freezing. Solvent-based (oil/alkyd) lasts up to 15 years. Sign of a bad can: a strong sour smell, or solids that will not re-disperse with stirring.

Disclaimer

Estimates assume a smooth, primed, non-absorbent surface. Bare wood, fresh drywall, and textured walls will consume 20–50% more paint for the first coat. Coverage rates are manufacturer claims and assume professional application.

Paint Coverage Calculator

Details

Embed this calculator

Share this calculation

Recommended Next

Unit Price Calculator

Recipe Scaler

Solar Panel Sizing Calculator

Was this calculator helpful?

No

Inputs

Results