Abstract: A bimetal unit for a circuit breaker is disclosed, the bimetal unit including a bimetal element for releasing a trip mechanism of the circuit breaker. In an embodiment, the bimetal element is surrounded, in particular coaxially surrounded, by a ferrous ring and a copper coil wound around the ferrous ring. The ferrous ring and copper coil provide a compensation device which produces additional heat and, as a result, stronger bending to the bimetal element when a current flows through the same bimetal element. An embodiment of the invention is useful to employ bimetal element adapted for higher-rated current in a circuit breaker of lower-rated current as bimetal element exhibits similar bending behavior as in higher-rated circuit breaker. This enhances calibration and reduces manufacturing costs. A trip unit, a circuit breaker, a series of circuit breakers, and a method for calibrating a circuit breaker employing the bimetal unit, are also disclosed.