Paint coverage: walls, ceiling, doors/windows
Wall area 2×(L+W)×H minus doors 1.9m² and windows 1.5m². Divide by coverage m²/L, times coats, ceil to cans. One coat rarely enough. This calculator is designed for quick, private, offline use in your browser. All formulas run locally and are verified against official sources. You enter the core numbers, see the result instantly, and can check the steps, so you avoid the common mistake of applying a percentage to the wrong base or mixing units. Keep the inputs in the same unit system, verify the rate or factor for your country, and compare the result with a second example to catch typos before you save or file. Paint estimates start with wall area: 2×(length+width)×height peels off the ceiling if you are not painting it. Subtract doors (~1.9 m²) and windows (~1.5 m²) because you will not roll over them, then
TL;DR
- Perimeter×height = wall, subtract openings, net / coverage per coat, × coats, round up to 1L/5L.
- Formulas: Wall=2(L+W)×H | Net=Wall-Doors1.9-Windows1.5 | Liters=Net/Coverage×Coats
- 4×5 H2.7 — Net 45.2
How it works
Perimeter×height = wall, subtract openings, net / coverage per coat, × coats, round up to 1L/5L. 45.2m² 10m²/L 2 coats →9L. Start with clean inputs, keep the same units, and follow the order the formula shows. The tool does the arithmetic, but you decide the rate, period, or factor. A second example with different numbers shows how the result scales, which is the fastest way to spot a misplaced decimal or a monthly versus annual confusion before you act on the number. Paint estimates start with wall area: 2×(length+width)×height peels off the ceiling if you are not painting it. Subtract doors (~1.9 m²) and windows (
The math
4×5 H2.7 1door1window: wall48.6 net45.2 2 coats 9L →2×5L. 3×3 H2.5 no openings 1 coat 12m²/L →2.5L→3×1L.
Ceil because cannot buy fractional can. Add 10% rough walls.
Examples
4×5 H2.7
- Net 45.2
- 9L
3×3 H2.5
- 2.5L →3L
When to use it
✦ Renovation
Buy correct cans.
✦ Quotes
Painter estimates.
⚠ Common mistakes
- Not subtracting doors/windows
- Single coat when need two
FAQ (6)
Coverage?
Check can 10-14 m²/L wall, rough lower.
Ceiling?
Add L×W if painting ceiling.
Do you save the numbers I type for area, volume or conversions?
Not at all. Every conversion — kg to lbs, area, fraction math — runs locally. No form data is posted anywhere. You can convert 1,500 kg to lbs on a shared computer and walk away knowing nothing was logged.
Will it work without internet in class?
Yes — that's why students like it. Load once on Wi-Fi, then fraction, base-converter or standard deviation work offline in class or in an exam hall without signal. It's just math in JavaScript, no server round-trip.
How accurate are the math results?
We use standard definitions (e.g. 1 kg = 2.20462 lbs, BIPM SI) and double-check edge cases via automated tests. For homework or site measurements it's more than enough, but for certified engineering or lab work, cross-check with the primary standard.
Can I share a calculation with a classmate?
Tap 'Share Link' — it puts the inputs in the URL. Your classmate opens it and sees the same 3/4 → 0.75 → 75% breakdown instantly, without retyping.
Sources & References
How this calculator is maintained
This calculator is written and maintained by Davide Coronese, independent developer and founder of CalcTracker.
Methodology: every formula is checked against official publications and validated by an automated test suite before release. Health, tax and finance pages cite the exact sources they rely on.
Found an error? Contact us — verified corrections ship within 24 hours.