The choice of the pixel resolution for the production of the digital elevation model (DEM) using Structure from Motion (SfM) software can largely influence the time of data treatment and the required data storage capacity. The objective of this study was to investigate the effect of the DEM resolution on height measurements of five perennial forage species. Images were acquired with a UAV, model Phantom 4 Advanced (DJI, China). Three flights were repeated 5 days apart in June 2018 on a trial involving pure stand microplots of two grass (orchard grass and tall fescue) and three legume species (alfalfa, red clover and white clover). The flights occurred at an altitude of 9 m above the ground to achieve an image resolution of 2 mm. The DEMs were built with a pixel resolution of 2, 4 and 8 mm using the SfM software Agisoft Photoscan (Agisoft Ltd, Russia). The results were compared to the height measured manually with a ruler at the same time as UAV acquisitions. The effect of DEM resolution on height measurements differed according to the species. For the three legume species, similar and reliable regressions between manual and UAV height measurements were obtained with the three tested resolutions for the three dates (0.88 < R² < 0.97). The most reliable regressions were obtained for the orchardgrass (R² > 0.81) with a DEM resolution of 4 mm. The results obtained for tall fescue were less reliable than for the other species. The highest regressions between manual and UAV height measurements for this species (0.56 < R² < 0.71) were obtained with the lowest DEM resolution (8 mm)