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Biomass feedstocks are often fluidized in thermochemical conversion systems that are used to breakdown biomass into low molecular weight compounds. Fluidization equations such as Ergun equation are used to determine fluidization conditions by incorporating the values of the physical properties (e.g. diameter) of the material of interest in these equations. However, because biomass grinds have non-uniform and non-spherical particles, equivalent diameter values are dependent on the size measurement method. This study investigates how the equivalent diameters obtained from the size measurement methods affect the ability of five fluidization equations to predict the minimum fluidization velocities (Umf) of fractions loblolly pine grinds. The behavior of loblolly pine wood grinds during fluidization was also assessed. Loblolly pine chips that were ground through 1/8" (3.18 mm) screen size were fractionated using six standard sieves that ranged between 0.15 mm and 1.7 mm. Particle density, bulk density, sphericities and equivalent diameters (based on minimum Feret, Martin, chord and surface-volume size measurement methods) for each fraction were measured. Size measurement method was found to significantly influence equivalent diameters of the grinds (p <0.05). Highest value of equivalent diameter was obtained when minimum Feret diameter was measured. The Umf of loblolly pine wood grinds (unfractionated samples) was found to be 0.25 ±0.04 m/s while the Umf of fractionated samples increased with increase in particle size from 0.29 m/s to 0.81 m/s. The lowest mean relative deviation values of predicted Umf from experimental Umf was obtained when equivalent diameter from Martin diameter size measurement method was used in the fluidization equations. [ABSTRACT FROM AUTHOR]