Paint Calculator
Not sure how much paint to buy? Enter your room's dimensions (or the total wall area), subtract doors and windows, choose your number of coats, and this free paint calculator tells you exactly how many liters or gallons you need — rounded up to whole cans, in metric or imperial units.
How this paint calculator works
The calculator adds up your four walls (2 × (length + width) × height),
subtracts the area taken up by doors and windows, then multiplies by the number of coats
to get the total surface to cover. Dividing that by your paint's coverage rate gives the
volume needed, which is rounded up to the nearest whole
liter so you don't run short. Default opening sizes assume a
standard door (about 1.8 m² / 20 ft²) and window (about 1.5 m² / 15 ft²) —
adjust them to match your room. Coverage varies by paint and surface; rough, porous or
unprimed walls soak up more, so buy a little extra for touch-ups.
Frequently asked questions
How much paint do I need for a room?
Measure the total wall area (wall perimeter × ceiling height), subtract doors and windows, multiply by the number of coats, then divide by your paint's coverage. Most wall paints cover about 10 m² (roughly 350 ft²) per liter or gallon, per coat.
How do you calculate wall area?
For a rectangular room, wall area = 2 × (length + width) × height. Enter the
room's length, width and height above and the tool does the math automatically. If you've
already measured the walls, switch to "By wall area" and type the total directly.
How much area does a liter or gallon of paint cover?
A typical wall paint covers about 10–12 m² per liter, or 350–400 ft² per US gallon, for one coat on a smooth, primed surface. Check the coverage printed on your can and enter that number for the most accurate estimate.
How many coats should I apply?
Two coats is the usual choice for an even, durable finish. One coat can work when refreshing a similar color over a good surface. Add a separate primer coat when painting over dark colors, bare drywall or stains.