Novel mechanical separations use centrifugation after expansion cooling to separate the contaminants (carbon dioxide and/or hydrogen sulphide) out of natural gas. The size of condensed carbon dioxide (CO2) enriched droplets after expansion cooling determines the design of these centrifugal separation units. We report the first measurements of condensed CO2 enriched droplets using an optical reflectance method. CO2 droplets in a methane enriched atmosphere down to 2 mu m are detected. The optical reflectance method directly yields a chord length distribution rather than the actual diameters. A complete scheme to interpret the diameters from these raw signal (chord length distribution) measurements is presented. The scheme is validated experimentally by comparison with light diffraction measurements to calibrate the optical reflectance probe.