In this work, an evaluation method to calculate the austenite fraction during continuous heating and isothermal annealing from dilatometric data is proposed. By means of a single reference measurement to determine a scaling factor correcting for experimental errors, a framework is created to determine the austenite fraction as a function of time and temperature. In the evaluation of the dilatometric data the effect of the changing carbon concentration in austenite phase is taken into account. The method is applied to dilatometric data for a 0.16C-1.5Mn-0.4Si (wt%) low-silicon transformation induced plasticity (TRIP) multiphase steel. Three typical dilatometric data are obtained by heating the material to 750degreesC, 800degreesC or 900degreesC, which leads to three different microstructures consisting of (1) ferrite, cementite and austenite, (2) ferrite and austenite and (3) full austenite, respectively. The calculated results using the proposed new method are compared with the results from thermodynamic analysis and those from quantitative microscopic analysis. Significant inter-test discrepancies are observed.