This Digest is part of a suite of related documents containing guidance for the construction industry on structural fire engineering design. The intention is to produce performance based guidance that brings together fire engineering and structural engineering providing a framework within which designers are free to develop site specific solutions based on real performance criteria. The Digests contain information complementary to the existing and emerging fire engineering codes and standards. Each digest may be used in isolation or as part of the full integrated suite. This Digest provides information on methods to calculate the time-temperature response for building fires based on the physical characteristics of the fire compartment. The purpose of this Digest is to discuss the most relevant calculation methods in the UK and European standards, to recommend the most appropriate method for design and to provide worked examples and comparisons with experimental data.