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.
Other Project Calculators You May Find Useful
Planning a project that goes beyond just painting? You might also find these calculators helpful:
- Epoxy Calculator – great for estimating epoxy resin coverage for floors, countertops, or DIY projects.
- Resin Calculator – perfect for working out how much resin you’ll need for casting, art, or sealing projects.
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.
Important Estimate Disclaimer
The results provided by this calculator are intended as general estimates only and should not be considered precise engineering measurements. Actual material requirements, costs, and quantities can vary significantly based on site conditions, local building codes, soil type, reinforcement requirements, climate exposure, and the intended use of your project.
These calculators are designed to help you plan and budget your project more effectively, but they do not replace professional advice from a qualified contractor, engineer, or building inspector. Always verify your calculations and assumptions with trained professionals before placing material orders or commencing construction.
For more information on the assumptions, formulas, and data used in these tools, see our Data Sources and Methodology pages.
Material estimates, cost figures, and volume calculations are approximate and may not reflect your actual requirements. Always double-check dimensions and project-specific needs, and consider adding a contingency allowance for waste, over-excavation, and unforeseen conditions.
If you are unsure about any aspect of your project — including structural requirements, reinforcement needs, drainage, or load-bearing capacity — consult with a licensed professional before proceeding.