Abstract An indicator, namely equivalent hot side temperature (TEHST) is proposed for the organic Rankine cycle (ORC). TEHST is derived from ideal thermodynamic process, but can denote the efficiency of irreversible ORC. Study on 27 fluids shows that given the operating conditions, fluid of higher TEHST generally offers higher ORC efficiency. This relationship is stronger and more universal than those established with respect to the critical temperature, boiling point temperature, Jacobs number and Figure of Merit. An ORC model by the method of error transfer and compensation is further built, in which the efficiency is quantitatively correlated with TEHST. Unlike the conventional ORC efficiency model, this one consists of thermodynamic parameters on the liquid/vapor curve and is independent on fluid properties at superheated state, and hence is more convenient. It has high accuracy especially for basic ORC and the relative deviation of the estimated efficiency from that calculated by the conventional model is from −0.7% to 3.4%. The novel model is applied for the thermodynamic performance prediction of a recently developed fluid of HFO1336mzzZ based on the phase equilibrium data. The results indicate HFO1336mzzZ is more efficient than R245fa on the conditions of high evaporation temperature and low pump efficiency.