Paint Calculator

The paint calculator tells you exactly how many litres of paint to buy for any room. Enter the length, width, and ceiling height of the room, the number of doors and windows, how many coats you plan to apply, and the paint's coverage rate — the result is the litres needed plus a 10% buffer for waste and touch-ups. Buying too little means a second trip to the hardware store mid-project, often to find the batch has a slightly different tint. Buying too much leaves you with unused paint that is difficult to dispose of responsibly. Getting the number right before you shop saves both money and frustration. This calculator is most useful before starting any interior room — bedrooms, living rooms, kitchens, and bathrooms. For ceilings, run the calculation separately using length × width as a flat area (enter 0 for doors and windows). For exterior walls, the same formula applies; just measure the total facade and subtract each window and door opening.

How to Use the Paint Calculator

The Paint Calculator is designed to give you an accurate answer in seconds. Follow these steps:

1. Step 1: Enter your room length (m) in the Room Length (m) field. The minimum value is 0.1. The default is 5 m. Adjust this to match your specific situation.
2. Step 2: Enter your room width (m) in the Room Width (m) field. The minimum value is 0.1. The default is 4 m. Adjust this to match your specific situation.
3. Step 3: Enter your ceiling height (m) in the Ceiling Height (m) field. The minimum value is 1. The default is 2.4 m. Adjust this to match your specific situation.
4. Step 4: Enter your number of doors in the Number of Doors field. The minimum value is 0. The default is 1. Adjust this to match your specific situation.
5. Step 5: Enter your number of windows in the Number of Windows field. The minimum value is 0. The default is 2. Adjust this to match your specific situation.
6. Step 6: Enter your number of coats in the Number of Coats field. The valid range is 1 to 5. The default is 2. Adjust this to match your specific situation.
7. Step 7: Enter your paint coverage (m² per litre) in the Paint Coverage (m² per litre) field. The minimum value is 1. The default is 10 m²/L. Adjust this to match your specific situation.
8. Step 8: Click Calculate to see your results instantly. The output updates as soon as you submit.

No account or sign-up required. All calculations run locally in your browser — nothing is stored or transmitted to any server.

Example Calculation

Here is what the Paint Calculator produces with its default values. Change any input above to recalculate instantly for your own figures.

How It Works

Litres = ((2 × (L + W) × H) − Doors − Windows) × Coats ÷ Coverage

Formula: Litres = Net Wall Area × Coats ÷ Coverage Rate Net Wall Area = (2 × (Length + Width) × Height) − (Doors × 1.9 m²) − (Windows × 1.2 m²) The wall area formula calculates the perimeter of the room (all four walls combined) multiplied by height, then subtracts standard areas for doors (1.9 m² average for a standard interior door) and windows (1.2 m² average for a standard window). Example: 5 m × 4 m room, 2.4 m ceiling, 1 door, 2 windows, 2 coats, 10 m²/litre coverage. Perimeter area = 2 × (5 + 4) × 2.4 = 43.2 m² Net area = 43.2 − 1.9 − 2.4 = 38.9 m² Litres = 38.9 × 2 ÷ 10 = 7.78 L With 10% buffer = 8.56 L → buy 9 litres Coverage rate varies by paint type and finish. Emulsion and matt paints typically cover 10–12 m²/litre. Gloss and satin cover 9–11 m²/litre. Textured paints and primers cover less, often 6–8 m²/litre. Check the tin label for the manufacturer's stated coverage and enter that number for the most accurate result.

Frequently Asked Questions