Free tool
Tank Volume Calculator
Calculate your tank's volume in gallons or litres by entering your cistern's dimensions. Handy for sizing, water planning and your liner quote.
Formulas: rectangular = length × width × height. Cylindrical = π × radius² × height. Orientation doesn't change the total volume.
Example: a 6' × 4' × 4' tank is 96 cubic feet, about 718 US gallons or 2,718 litres.
Calculate your tank's volume
Enter your cistern's inside dimensions for an instant capacity estimate.
US gallons718
Litres2,718
Cubic metres2.72
Maximum capacity when full. Doesn't account for current water level, sediment or freeboard. Irregular or tapered cisterns need professional measurement.
Ordering a liner?
Liners are made to your cistern's actual dimensions, so measure the interior carefully. Our guide shows how.