Abstract: A method and device for measuring the required cooling capacity of a cold space is disclosed. The method includes the steps of cooling the cold space to a first low temperature below an ambient temperature, permitting the temperature of the space to rise to a second higher temperature below the ambient temperature during a first period, measuring the length of the first period, cooling the space again to the first low temperature during a second period, measuring the length of the second period, permitting the temperature to rise to a second higher temperature during a third period, heating the space during the third period by a known amount, and measuring the length of the third period to determine the thermal capacity of the space using the known amount of heating the measured first, second and third periods.