Abstract: A scale for mounting on a semi-trailer having an air bag in the suspension and an air line connected to the air bag includes a pressure transducer for connecting to the air line and measuring the pressure in the air bag, and to send a signal correlated to the sensed pressure, a process module in electric communication with the pressure transducer and configured to receive the signal therefrom wherein the process module is configured to correlate the signal from the pressure transducer to a weight of a load on the trailer, and a display module configured to receive a signal from the process module indicating the sensed weight and display the sensed weight of the load on the semi-trailer. A method for monitoring weight includes converting pressure in the air line to a weight of the semi-trailer, which can be monitored in real-time.