The light optical aerosols counter (LOAC) instrument is an optical aerosol counter that allows atmospheric particles from 0.2 to 50 µm to be individually counted and classified by size. The scattered light due to the interaction between a particle and a laser beam is captured by photodiodes and produces an electric pulse. Detecting these pulses and measuring their amplitude is a key process to measure the particle size. This paper first details the current method to achieve such estimation and proposes a correlation algorithm to improve the detection and the assessment of particle sizes. In the last section, some test results are presented to demonstrate the performance of this new algorithm.