Abstract The aim of this paper is to present a new numerical heat source for gas tungsten arc welding (GTAW) simulation. This source is described as a homogeneous thermal flux which is defined by a power P distributed in a disk the radius of which is R : it enables the main dimensions of the weld bead and the evolution in temperature in the solid part to be predicted. The two parameters P and R relate to the process parameters, the arc length h and the current intensity I . Experimental tests were performed in order to study the weld bead dimensions in incomplete penetration and full penetration welds. For each test, the heat source parameters ( P , R ) which enable the experimental weld bead dimensions to be obtained were identified: a link between the heat source parameters ( P , R ) and the welding parameters ( I , h ) was established and thus a predictive heat source was produced.