This document describes a calibration and verification method for a light scattering airborne particle counter (LSAPC), which is used to measure the size distribution and particle number concentration of particles suspended in air. The light scattering method described in this document is based on single particle measurements. The typical size range of particles measured by this method is between 0,1 μm and 10 μm in particle size. Instruments that conform to this document are used for the classification of air cleanliness in cleanrooms and associated controlled environments in accordance with ISO 14644‑1 and ISO 14644‑2, as well as the measurement of number and size distribution of particles in various environments. The following parameters are within the scope of this document: — size setting error; — counting efficiency; — size resolution; — false count; — maximum particle number concentration; — sampling flow rate error; — sampling time error; — response rate; — calibration interval; — reporting results from test and calibration.