At the heart of a load cell is a strain gauge. A strain gauge is a device that changes resistance when it is deformed or stressed. The precise positioning of the gauge, the mounting procedure and the materials used all have a measurable effect on overall performance of the load cell.

A strain gauge is then cemented to the surface of a beam, diaphragm or column within a load cell. As the surface to which the gauge is attached becomes strained, the fine wires of the strain gauge expand or compress changing their resistance proportional to the applied load. In most strain gauges, four gauges (or sometimes eight gauges) are used in the making of a load cell.

Multiple strain gauges are connected to create the four legs of a Wheatstone-bridge configuration. When an input voltage is applied to the bridge, the output becomes a voltage proportional to the load on the cell. The more load that is applied to the cell, the more the bridge becomes unbalanced and the larger the output. This output can be amplified and processed by signal conditioning or data acquisition equipment. In order to increase sensitivity of the Wheatstone bridge, all the arms are active and the four strain gauges are arranged so that two arms of the bridge are in compression while the other two arms are in tension.