Buying paint without measuring first is how most people end up with either a half-finished wall or three extra cans gathering dust in the garage. This free paint coverage calculator works it out properly: enter your room size, subtract the doors and windows, choose how many coats you plan to apply, and it tells you exactly how many litres of paint to buy.
Paint Coverage Calculator
Most emulsion paints cover about 100 sq ft per litre per coat. Check the label on your paint can and adjust this number if yours is different.
How to Use This Calculator
- Measure the room. Measure the length and width of the room in feet, and the height from floor to ceiling.
- Count doors and windows. A standard door is counted as 21 sq ft and a standard window as 15 sq ft, so you do not pay for paint you will never apply.
- Choose your coats. Two coats is the standard for a fresh colour. One coat may be enough over a similar existing colour; a dark-to-light change often needs three.
- Check your paint label. If your paint covers more or less than 100 sq ft per litre, update the coverage field before calculating.
- Buy the rounded-up amount. The result rounds up to whole litres, so you have a little extra for touch-ups.
Worked Example
A room 14 ft long, 12 ft wide and 10 ft high has 520 sq ft of wall. Subtract one door (21 sq ft) and one window (15 sq ft) and you get 484 sq ft to paint. At two coats and 100 sq ft per litre, that is 9.68 litres - so buy 10 litres.
Tips to Avoid Wasting Paint
- Prime first when painting over a dark colour or fresh plaster - primer improves coverage and can save a whole top coat.
- Buy all your paint from the same batch if possible, so the shade matches across every wall.
- Keep a small labelled jar of leftover paint for future touch-ups instead of storing a half-empty can.
- Measure twice: a wrong wall height is the most common reason paint estimates go wrong.
How this calculator works
This calculator works in four steps. First, it finds the total wall area from the room perimeter: wall area = 2 x (length + width) x height. Second, it subtracts the area you will not paint, using 21 sq ft for each standard door and 15 sq ft for each standard window in this tool. Third, it multiplies the remaining paintable area by the number of coats. Finally, it divides by the paint coverage from the label, in sq ft per litre, and rounds the answer up to whole litres, so you have a little extra for touch-ups.
Paint to buy (litres) = paintable area x coats / coverage, rounded up. The ceiling is not included, so if you plan to paint it, add length x width to the paintable area before you calculate.
Worked example
Take a room 10 ft long, 12 ft wide and 9 ft high, with 1 door, 2 windows, 2 coats and paint covering 100 sq ft per litre.
- Wall area = 2 x (10 + 12) x 9 = 396 sq ft.
- Deductions = 1 x 21 + 2 x 15 = 51 sq ft.
- Paintable area = 396 - 51 = 345 sq ft.
- Paint needed = 345 x 2 / 100 = 6.90 litres, so buy 7 litres.
That is the exact result the tool gives for these inputs: 6.90 litres, rounded up to 7 litres.
Quick reference: paint for two coats at 100 sq ft per litre
The table below uses 1 door and 1 window, and rounds up to whole litres, just as the tool does.
Room Paintable area Buy 10 ft x 10 ft, 8 ft walls 284 sq ft 6 litres 12 ft x 12 ft, 9 ft walls 396 sq ft 8 litres 14 ft x 12 ft, 10 ft walls 484 sq ft 10 litres 16 ft x 14 ft, 10 ft walls 564 sq ft 12 litres
Always check your own can: if its coverage is lower than 100 sq ft per litre, enter that lower number in the tool before buying.
Frequently Asked Questions
How this calculator works
This calculator works in four steps. First, it finds the total wall area from the room perimeter: wall area = 2 x (length + width) x height. Second, it subtracts the area you will not paint, using 21 sq ft for each standard door and 15 sq ft for each standard window in this tool. Third, it multiplies the remaining paintable area by the number of coats. Finally, it divides by the paint coverage from the label, in sq ft per litre, and rounds the answer up to whole litres, so you have a little extra for touch-ups.
Paint to buy (litres) = paintable area x coats / coverage, rounded up. The ceiling is not included, so if you plan to paint it, add length x width to the paintable area before you calculate.
Worked example
Take a room 10 ft long, 12 ft wide and 9 ft high, with 1 door, 2 windows, 2 coats and paint covering 100 sq ft per litre.
- Wall area = 2 x (10 + 12) x 9 = 396 sq ft.
- Deductions = 1 x 21 + 2 x 15 = 51 sq ft.
- Paintable area = 396 - 51 = 345 sq ft.
- Paint needed = 345 x 2 / 100 = 6.90 litres, so buy 7 litres.
That is the exact result the tool gives for these inputs: 6.90 litres, rounded up to 7 litres.
Quick reference: paint for two coats at 100 sq ft per litre
The table below uses 1 door and 1 window, and rounds up to whole litres, just as the tool does.
| Room | Paintable area | Buy |
|---|---|---|
| 10 ft x 10 ft, 8 ft walls | 284 sq ft | 6 litres |
| 12 ft x 12 ft, 9 ft walls | 396 sq ft | 8 litres |
| 14 ft x 12 ft, 10 ft walls | 484 sq ft | 10 litres |
| 16 ft x 14 ft, 10 ft walls | 564 sq ft | 12 litres |
Always check your own can: if its coverage is lower than 100 sq ft per litre, enter that lower number in the tool before buying.
How many litres of paint do I need for one room?
It depends on the room size, but a typical 12 by 14 ft room with 10 ft walls needs about 10 litres for two coats, after doors and windows are subtracted.
Is one coat of paint enough?
Only if you are repainting the same or a very similar colour over a surface in good condition. For a colour change, plan on two coats.
Does the ceiling count?
This calculator covers walls only. For a ceiling, add its area (length times width) to your paintable area and calculate again, or use ceiling paint separately.