How to use Room Paint Calculator
Estimate wall paint, extra allowance and whole containers from label coverage.
- Measure every wall and add the area of openings you plan to exclude.
- Read the coverage range and coat instructions on your exact product.
- Compare litres with the available container sizes before ordering.
Formula & calculation method
Net wall area = 2 × (room length + width) × height − openings. Litres = net area × coats ÷ label coverage × (1 + allowance ÷ 100). Containers are rounded up.
Input reference · 8 fields
These labels describe the calculation’s base units. Supported measurements can switch through the header’s region settings; follow the current workspace labels. Prefilled values are examples.
- Room length (m)
- Enter a plain number with a decimal point if needed. The workspace shows an illustrative value, not a recommendation.
- Room width (m)
- Enter a plain number with a decimal point if needed. The workspace shows an illustrative value, not a recommendation.
- Wall height (m)
- Enter a plain number with a decimal point if needed. The workspace shows an illustrative value, not a recommendation.
- Total door/window area (m²)
- Enter a plain number with a decimal point if needed. The workspace shows an illustrative value, not a recommendation.
- Number of coats
- Enter a plain number with a decimal point if needed. The workspace shows an illustrative value, not a recommendation.
- Coverage per coat (m² / litre)
- Use the coverage printed on the product label.
- Extra allowance (%)
- Enter a plain number with a decimal point if needed. The workspace shows an illustrative value, not a recommendation.
- Container size (litres)
- Enter a plain number with a decimal point if needed. The workspace shows an illustrative value, not a recommendation.
A quick example
A 5 m × 4 m room at 2.5 m height has 45 m² of walls. Subtract 4 m² openings: 41 m². Two coats at 10 m²/L need 8.2 L; adding 10% gives 9.02 L, or four 2.5 L containers.
Assumptions, edge cases & limits
- Ceilings, primer and trim are excluded. Product coverage, substrate and application vary. Use label coverage; an allowance is your assumption, not a guarantee.
- Only the four walls of one rectangular room are modeled; add ceilings or irregular surfaces separately.
Questions about Room Paint Calculator
Does the paint estimate include doors and windows?
Enter their combined area in the openings field to subtract it from the walls. Do not subtract an opening twice. The model covers rectangular walls, not ceilings, and uses your chosen coats and product coverage.
How many paint containers should I buy?
The tool divides the calculated paint volume, including your extra allowance, by container size and rounds up. Check the paint label’s actual coverage and whether another coat is needed.
Are my files or inputs uploaded?
Calculation and file processing run in your browser without a processing upload. Downloads go to your device. Choosing a next-step transfer creates a temporary local copy for that workflow. Region preferences are stored separately from tool inputs. See our privacy details.
Can I use this tool for free?
Yes. No signup, subscription or payment is required to use the tool or download its output. File tools have device and size limits; a smaller batch may work better on a phone.
Method & references
Read the underlying method or measurement convention in context. These references do not imply affiliation or endorsement.
Sherwin-Williams: paint calculator guidance ↗Check the assumptions, measurement conventions and actual product or contract terms for your use case.A result or explanation needs correcting? Tell us the tool name and an example.