Planar two-dimensional two-colour time-resolved laser-induced incandescence (2D-2C-TiRe-LII) is employed to investigate soot formation in a standard ethylene laminar di usion ame. The time resolution of the 2D LII signal is realised by shifting the delay time of ICCD cameras. The two-colour con guration is applied to measure the peak temperature Tp of soot particles immediately after the laser pulse rather than using the energy balance to compute Tp. The Sauter mean diameter D32 and the corresponding distribution width parameter of the measured soot particles is extracted by using an error minimisation method. The method shows that a range of possible geometry mean particle diameters and corresponding distribution width parameters are also possible solutions, and further information on realisable particle size distribution widths is necessary to narrow down the extracted diameter.