Your tank will hold 1160 Liters. How far above the tank will you mount the ultrasonic transducer? You need to have it at least 3 - 4 cm above the top of the tank. Then measure the distance from the transducer to the bottom of the tank. Subtract the transducer reading from that and you will have the height of the liquid. Then it is simply pi * r * r * h * 1000 for liters.
Note: r and h are in meters.
If the above dimensions are the actual tank, pi * r * r * 1000 will be 1075. Just multiply the height of the liquid by that for liters. There will be a slight error due to rounding. (1075 * 1.08 = 1161)
(Have not figured out Pi or superscript symbols on this forum)