Plan your paint purchase
Paint Calculator for Walls & Ceilings
Quick mode handles one surface. Advanced adds rooms, openings, multiple surfaces and can sizes.
Enter your measurements and the coverage from the paint label. We’ll estimate the volume you need and suggest a combination of whole cans.
Result
This is a planning tool, not a professional estimate or a guarantee of actual paint use. Actual use depends on the product, surface, preparation, and application. Check the coverage, number of coats, and instructions on the product label or technical data sheet. The waste allowance is your input. Package recommendations use only the can sizes and prices you enter; they do not confirm store availability. Currency is a label only; no exchange conversion is performed.
Check the calculation
How the paint estimate works
Every step is shown so you can check the numbers before buying paint. The calculator uses the measurements, coverage, coats, waste allowance and can sizes you enter; it does not assume product details or store availability.
Formula
The estimate follows the same calculation order shown in the result.
- Net paintable area = total measured surface area − excluded openings.
- Theoretical paint = net paintable area × number of coats ÷ coverage.
- Paint including waste = theoretical paint × (1 + waste allowance ÷ 100).
- Purchased paint is the selected combination of whole cans that meets or exceeds the required amount under the selected strategy.
- Remainder = purchased paint − paint including waste.
Variables
- Net area
- Measured paintable area after the openings and excluded rectangles you enter are subtracted.
- Coats
- The whole number of paint coats you plan to apply.
- Coverage
- The area covered by one litre or U.S. gallon from the product label or technical data sheet.
- Waste allowance
- The percentage you add for expected waste. The calculator does not add a waste value on its own.
- Can sizes
- The can sizes you enter for the purchase recommendation.
Worked example
This example uses metric units and the least-remainder purchase strategy.
- Inputs: 57.8 m² net area, 2 coats, 10 m²/L coverage, 7% waste allowance, and one 2.5 L can size.
- Net paintable area: 57.8 m².
- Theoretical paint: 57.8 × 2 ÷ 10 = 11.56 L.
- Paint including waste: 11.56 × 1.07 = 12.3692 L.
- Purchased paint: 5 × 2.5 L = 12.5 L.
- Remainder: 12.5 − 12.3692 = 0.1308 L.
With only one can size available, the fewest-cans strategy also selects these five cans. Lowest cost is unavailable because no price was entered.
Values you choose
- Enter coverage from the exact paint product label or technical data sheet.
- Choose the number of coats required for the product, colour change, and surface condition.
- Enter a waste allowance that suits your preparation and application method.
- Enter only the can sizes available to you; the recommendation uses no hidden package data.
Limitations
- Actual use can change with product, substrate, texture, porosity, preparation, colour change, application method, and loss on tools.
- The calculation includes only the rectangular surfaces and exclusions you enter. It does not account for their positions or for details you leave out.
- Price and currency do not change the physical paint requirement; currency is only a label and is not converted. The calculator does not confirm stock, regional package sizes, or store availability.
Frequently asked questions
How much paint do I need for a room?
Measure the walls and ceiling you plan to paint, subtract any openings, and enter the number of coats and coverage from the paint label. The calculator then estimates the volume and whole cans to buy.
How many coats should I enter?
Enter the number of coats required for the product, surface, or colour change. The calculator does not choose this value for you.
Should I subtract doors and windows?
Yes. In Advanced mode, enter each measured rectangular opening or excluded area. The calculator uses only the dimensions you enter.
Why can the amount to buy be higher than the calculated amount?
Your waste allowance increases the paint requirement, and paint is bought in whole cans. Both can make the purchased amount higher.
Is the data I enter sent anywhere?
No. The calculation runs in your browser; the data you enter and the results are not sent to a server.