The occurrence of volcanic lightning during explosive eruptions is a common phenomenon, yet the exact mechanisms of electric charge transmission in explosive eruption columns and plumes are poorly understood. Ash is a probable charge carrier and so the physical properties of ash may factor into charge transmission, specifically, the shape and size of ash grains. To examine the relationship between volcanic ash electrical conductivity and particle size and shape, this research compares conductivity measurements to grain size distributions and shape parameters from several volcanic centers. Grain size distributions were measured using a laser diffraction particle size analyzer (LDPSA); grain shapes (e.g., aspect ratios, solidity) were characterized using backscattered electron images. The volume resistivity of minimally compressed samples was measured at controlled temperature (25-30 ℃) and relative humidity (25 %) using a current amplifier and values were converted to conductivity. A general effective media (GEM) equation was then applied to account for variations in grain packing, grain shape, and sample porosity. Although all ash samples are electrically insulating, homogenized samples provided maximum conductivity measurements that ranged over roughly four orders of magnitude (10-9 – 10-13 S/cm); non-homogenized bulk Alaskan sample conductivity values ranged over roughly six orders of magnitude (10-9 – 10-15 S/cm). Results indicate that size has a greater effect on ash conductivity than shape. Results also suggest that particle size distribution controls ash conductivity, as samples with a wide distribution of particle sizes and larger surface areas, due to a combination of fine and coarse grains, will have the highest conductivity values. Therefore, the efficiency of magma fragmentation during explosive eruptions, and the resulting proportions of fine and coarse ash particles generated, controls the bulk electrical conductivity of volcanic ash and may contribute to charge transmission mechanisms in eruptive columns and plumes.