Particle shape affects particle size measurements from different analyzers. Spherical and blocky particles give similar results with an optical microscope and a Coulter counter, but prismoidal and platy particles differ. Laser diffraction method shows agreement for spherical, blocky, and platy particles, but cubical and prismoidal particles vary. A technique was developed to estimate mean particle size using an optical microscope from Coulter counter or laser diffraction results, allowing comparison without shape influence.