Background and objectives Particle size distribution and damaged starch content have a major impact on flour quality because they influence the behavior of flour during hydration in processing. Particle size distribution and starch damage of legume flours and their relationship during grinding have not been evaluated. The standard enzymatic method for the measurement of damaged starch content (AACC 76-31) was used to find a new calibration equation for the rapid amperometric method (SDmatic, AACC 76-33.01) for legume flours. Changes in particle size distribution and starch damage during regrinding in a commercial pea flour were compared with those in a commercial wheat flour. Findings Legume flours had a smaller damaged starch content (0.8-4.7 SD%) than wheat flours (2.2-7.0 SD%). The bimodal particle size distribution of flours was linked to structural elements as confirmed by environmental scanning electron microscopy and laser granulometry. Particle size distribution and starch damage varied concomitantly during regrinding in the commercial pea flour as in the commercial wheat flour. The main factor responsible for the increase in damaged starch content was an increase in the proportion of the fine fraction in the flour. Fine fractions contained higher damaged starch contents than coarse fractions. Conclusions Hypotheses concerning differences in fragmentation mechanisms in the two flours were formulated, suggesting that pea flour has a higher likelihood for fracture but less tendency to produce damaged starch than wheat flour. Significance and novelty The amperometric method (AACC 76-33.01) can be used for a rapid estimation of the damaged starch content in legume flours. Furthermore, the results suggest a lower hardness of pea flour material compared to wheat flour material that would have a significant impact on milling strategies.