Paint Calculator – How It Works
Our paint calculator is designed to take the guesswork out of planning your painting project. By entering your room’s length, width, and height, the tool calculates the total wall surface area. It then subtracts standard openings like doors and windows, applies the number of coats you’ve selected, and divides by your paint’s coverage rate. This ensures you get an accurate estimate of how many litres or gallons you’ll need.
You can also choose to include ceilings and trim, which many calculators leave out, giving you a more realistic picture of your total paint requirements. Results can be shown in either metric or imperial units, along with suggested can sizes so you know exactly what to buy.
Coverage & Real-World Factors
- Smooth, previously painted walls usually cover at 10–12 m² per litre (≈ 350–400 ft² per gallon).
- Unpainted, rough, or textured surfaces may need more paint or a primer coat.
- Darker colors or drastic color changes often require an extra coat for proper coverage.
- It’s best to allow for 5–10% extra for touch-ups, trims, and mistakes.
Tips for Buying Paint
- Round up to the nearest can size to avoid running short mid-project.
- Match sheen and brand for a consistent finish across all walls.
- Label leftover paint with the room name and date for easy touch-ups later.
- When in doubt, keep an unopened can—you can usually return it if unused.
Related Interior Calculators
Frequently Asked Questions
How do I include the ceiling?
Toggle Include Ceiling in the calculator, and we’ll add Length × Width
multiplied by the ceiling coats you select.
What about trim and baseboards?
Toggle Include Trim and the calculator will estimate based on your perimeter
and trim height (defaults are provided if you’re unsure).
Do darker colors need more paint?
Yes. Darker shades and bright colors usually require at least one additional coat,
or a tinted primer underneath for better results.
Accuracy & Review
Reviewed by: Natalie Green
Natalie reviews our paint-related calculators, validating coverage rates, coat count assumptions, and product yield calculations. She focuses on ensuring estimates align with real-world application results across interior and exterior projects.
Last updated:
See: Methodology · Data Sources · Review Board
Important Estimate Disclaimer
Results are provided for general planning and budgeting purposes only. Actual coverage may vary based on surface condition, layout complexity, waste allowance, and product specifications.
Refer to our Methodology and Data Sources for calculation assumptions.
Surface preparation, substrate irregularities, and installation methods may increase required material quantities.