Paint Calculator
Enter your room dimensions and calculate the paint quantity and number of cans needed.
Paint Calculator: How Many Litres for Your Room?
The most common mistake when buying paint is using the gross wall area. Paint bought without accounting for doors, windows and waste either runs out mid-room or sits unused in the garage. The paint calculator automatically computes the net wall area and gives you a realistic litre and tin count.
What Is a Paint Calculator and Why Do You Need One?
A paint calculator combines room dimensions, door/window areas, number of coats and waste factor into a single formula to estimate litre consumption. Given that paint tins come in various sizes (2.5 L, 5 L, 7.5 L, 10 L, 15 L), finding the optimum tin combination saves money.
Buying too much paint creates both cost and shelf-life problems; buying too little makes it hard to find the same colour batch later. The calculator suggests two tin combinations — economical and practical.
How to Use It. Step by Step
Required Inputs
- Room length and width (in metres)
- Ceiling height (in metres)
- Number of doors and windows
- Number of coats (1–3)
- Paint coverage rate per litre (m²/L)
- Waste factor (default 10%)
Formula / Calculation Logic
Wall area: 2 × (length + width) × height. 1.8 m² is deducted per door and 1.2 m² per window. Net area is multiplied by coats, divided by coverage rate, and the waste factor is added.
Example Scenario
| Parameter | Value |
|---|---|
| Room length | 5 m |
| Room width | 4 m |
| Ceiling height | 2.70 m |
| Number of doors | 1 (1.8 m²) |
| Number of windows | 2 (2.4 m²) |
| Net wall area | ≈ 44.1 m² |
| Coats | 2 |
| Total paintable area | ≈ 88.2 m² |
| Coverage rate | 10 m²/L |
| Waste factor (10%) | ≈ 10% |
| Paint required | ≈ 9.7 litres |
Tips for an Accurate Result
- Measure walls yourself — m² figures in deeds or lease agreements show floor area, not wall area.
- Enter the coverage rate 10–15% below the theoretical figure on the label; real-world consumption is always higher.
- If changing colour (dark to light or vice versa), raise the waste factor to 15%.
- Once you know the tin count, buy from the same batch number — colour can vary between lots.