To design a steel structure in fire is necessary to know its temperature. Using the data from many experimental fire tests, Margaret Law estimated the maximum temperature in a compartment (natural fire), the external heat transfer to steel elements and the maximum temperature value for steel. The Eurocode adopted her method, with minor adjustments. The method is very calculation intensive—it involves about 60 equations— too many for a quick hand calculation. Besides, while a distinction is made between steel members engulfed and not engulfed in flame, the method is not clear about partially engulfed members. The authors developed the software ExteelFire to determine the maximum temperature of external steel structures for buildings in fire based on the Eurocode method including the determination of the temperature of the partially engulfed elements. Aiming to ascertain the level of safety of the Eurocode method, the results from ExteelFire and a numerical analysis performed using Smartfire (CFD software for the fire model) and Super Tempcalc (finite element method, FEM, software for the thermal analysis) were compared. Furthermore, results from ExteelFire and from two full-scale experimental tests (Dalmarnock and Ostrava) were contrasted. Based on the comparisons, the Eurocode method is conservative.