The paper considers the optical contact-free method of droplet diameter sizing in the flow cross-section utilizing light interference on a droplet. Distribution of light scattered by a particle was analyzed for different configurations of the measurement system using the Mie theory and approximation of geometrical optics. Basic measurement errors and dynamic range were determined including the case of camera mounted at the angle of 90º to the plane of a laser sheet. With the use of obtained results a set of algorithms are suggested for processing of data obtained during experiment. Validation of IPI technique was carried out by means of comparison with direct observation method. The suggested approaches were applied for measurement of characteristics of the gas-droplet jet