A system and method for calculating parameters for a refrigeration system having a variable speed compressor is provided. A compressor is connected to a condenser and an evaporator. An evaporator sensor outputs an evaporator signal corresponding to at least one of an evaporator pressure and an evaporator temperature. An inverter drive modulates electric power delivered to the compressor to modulate a speed of the compressor. A control module is connected to the inverter drive that receives the evaporator signal. The control module monitors electrical power data and compressor speed data from the inverter drive and calculates at least one of a condenser temperature and a condenser pressure based on the evaporator signal, the electrical power data, and the compressor speed data.