Using the Paint Calculator
Use metres for room dimensions and square metres for the combined doors and windows. Enter coverage per litre for one coat from your paint label, then choose the pack size and its price in your currency.
Worked example
Use the example inputs below to reproduce this result. These are the form's starting values, not recommended targets. Changing your inputs updates your result above; this worked example stays fixed for comparison. Results are rounded for display.
Example inputs
- Room length (m)
- 5
- Room width (m)
- 4
- Wall height (m)
- 2.5
- Include ceiling?
- No
- Total door/window area (m²)
- 5
- Coats
- 2
- Coverage per litre per coat (m²/L)
- 10
- Extra allowance (%)
- 10
- Pack size (L)
- 5
- Price per pack (your currency)
- 30
Example result
- Net surface area (m²)
- 40
- Paint needed incl. waste (L)
- 8.8
- Packs to buy
- 2
- Paint purchased (L)
- 10
- Estimated leftover (L)
- 1.2
- Paint cost
- 60
Method and assumptions
Wall area = 2 × (length + width) × height. Add ceiling if selected, subtract openings, then multiply by coats / coverage and by (1 + allowance/100). Round up to whole packs. Excludes primer, labor and tools; use the paint manufacturer’s coverage for your surface.
Reference: omnicalculator.com — method and further reading
Turn an estimate into an order
A geometric quantity is a starting point for purchasing. Check whether the supplier sells by bag, box, mass or bulk volume, and use the stated coverage or yield to convert the result. Round only after accounting for the chosen allowance and packaging increments. For irregular spaces, divide the job into simpler sections and combine quantities with the same units.
Common question
Why is the purchased quantity larger than the estimated paint needed?
The estimate first adds your chosen allowance and then rounds the requirement up to whole packs. The leftover is the purchased quantity minus that estimated requirement, assuming you buy only the selected pack size.