This paper presents the design of a calorimeter for measuring losses in power electronics and electrical machines, including devices under test (DUTs) with active liquid cooling. The current calorimeter has a double jacketed structure with aluminium plates to minimise the heat leakage to the exterior through the walls. Heat leakage paths such as power cables and shaft hole were simulated in ANSYS to estimate the power loss, but these values will be validated and compensated during calibration of the unit. The measurement range is 5 kW, with a resolution of 80 mW at 120 W and 3 W at 5 kW. The heat leakage due to the shaft hole and power cables was estimated in ANSYS to be 1.4 W and 1.7 W respectively in the worst case.