Particle size distributions, measured by the forward scattering spectrometer probe (FSSP 300), are used in Mie calculations to specify polynomial expressions by which polar stratospheric cloud (PSC) extinction data can be converted into volume and area density values for type I, liquid phase PSCs. The calculations are carried out at the wavelengths observed by experiments on the Upper Atmosphere Research Satellite (UARS) and at the stratospheric aerosol measurement (SAM II), stratospheric aerosol and gas experiment (SAGE II), and polar ozone and aerosol measurement (POAM II) wavelength of 1 μm. The calculations use laboratory indices that approximate values for ternary solution and sulfuric acid droplets. Validation calculations intercompare the SAM II and FSSP 300 area densities, and SAM II and cryogenic limb array etalon spectrometer (CLAES) area densities. ¿ 1998 American Geophysical Union