A liquid-level sensing instrument for determining the level of a liquid in a container or vessel such as a laboratory tube in a rack or a well in a well plate with the container having an acoustically transparent top opening to direct ultrasonic signals to the liquid surface and receive reflected signals where the transceiver sensor instrument is constructed with a piezoelectric focusing sensor that has a concave focusing surface for focusing ultrasonic signals through the opening to the liquid surface in a selected container particularly a container in a group of containers and receiving reflected signals for processing.