How to use this paint calculator
- Units, choose Metric (metres and litres) or Imperial (feet and gallons).
- Room size, enter the length, width and wall height of the room.
- Openings, set the number of doors and windows so they can be subtracted from the wall area.
- Coats and coverage, pick how many coats you are applying and the coverage printed on your paint tin.
- Read the paint needed and the suggested amount to buy, they update instantly as you type.
Nothing is submitted or stored: the numbers never leave your device, so you can plan your project privately.
How much paint you need
The wall area is the perimeter of the room times the wall height. For a rectangular room that is2 × (length + width) × height. From that total you subtract the area taken up by doors and windows, because you are not painting those. This calculator uses a standard allowance of about 1.8 square metres per door and 1.5 square metres per window (roughly 19 and 16 square feet) so you do not have to measure each one.
Next, multiply the paintable area by the number of coats, then divide by the coverage of your paint. As a rule of thumb, one litre covers about 10 square metres per coat, and one gallon covers about 350 square feet per coat on a smooth, sealed surface. Rough, porous or freshly plastered walls soak up more, so check the figure on the tin and lower the coverage if the wall is thirsty.
Buy a little extra
It is worth buying about 10 percent more paint than the bare calculation suggests. That spare covers touch-ups, uneven absorption around edges and corners, and small repairs months later. Paint from the same batch also matches better than a tin bought separately, so a small surplus now saves a mismatched patch down the line. The "suggested to buy" figure already includes this 10 percent margin for you.
Frequently asked questions
How much paint do I need for a room?
Take the perimeter times the wall height for the wall area, subtract doors and windows, multiply by the number of coats, then divide by your paint's coverage. One litre covers about 10 square metres per coat, one gallon about 350 square feet per coat.
How many coats should I apply?
Two coats is standard. Use one for a refresh of the same colour, and three when a light colour has to cover a dark one or a strong stain.
Why does the result include extra paint?
The suggested amount adds about 10 percent for touch-ups, uneven coverage and future repairs, and keeps your colour matched to one batch.
Is my data uploaded?
No, everything is calculated on your device and nothing is sent anywhere.