Water Tank Capacity Calculator
Calculate the capacity of a cylindrical or rectangular water tank.
Assumptions used in this calculation
- Ideal geometric shape: Assumes a perfect cylinder or rectangular box, tanks with rounded corners, sloped bottoms, or irregular shapes will hold slightly less than the calculated volume.
- Full-capacity volume: Reports the tank's geometric capacity at full fill, not the usable volume, real tanks are typically not filled to the absolute brim in practice.
About this calculator
Choosing the right water tank size, or checking whether an existing one meets a household's or building's daily demand, requires converting physical dimensions into a usable volume figure, and the formula differs depending on whether the tank is round or box-shaped. This calculator applies the cylinder volume formula (πr²h) for round overhead or sump tanks, or the simple length × width × height formula for rectangular tanks, then converts the result from cubic metres into litres and gallons so the figure is usable regardless of which unit your supplier or plumber quotes in. Enter the tank's dimensions once, and get all three volume units back immediately instead of computing the geometry and then converting units separately. Because it reports the tank's full geometric capacity at the absolute brim, real-world usable capacity is typically somewhat less once you account for tanks that aren't filled completely or have rounded internal corners.
Worked example
Cylindrical tank, 2m diameter, 3m height
Result: ≈ 9,425 litres
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