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Further research is required on the measurement of crop evapotranspiration (ET_c) to produce new or updated crop coefficients for a large number of crops using accurate weighing lysimeters. However, large weighing lysimeters are sometimes expensive and are not portable, and different prototypes of small-sized lysimeters may be a feasible alternative. This study evaluated the performance of a removable mini-lysimeter model to measure ET_c and derive crop coefficients using a long-established large precision weighing lysimeter over a two-year period. The study was conducted during the 2017 and 2018 barley and potato growing seasons, respectively, at a lysimeter facility located in Albacete (southeast Spain). ET_c values were determined using daily mass change in the lysimeters. Irrigation was managed to avoid any water stress. In the barley season, the mini-lysimeter underestimated the seasonal ET_c by 2%, the resulting errors in barley ET_c estimation were an MBE of −0.070 mm d⁻¹ and an RMSE of ±0.289 mm d⁻¹. In the potato season, the mini-lysimeter overestimated the cumulative ET_c by 5%, the resulting errors in potato ET_c measurement were an MBE of 0.222 mm d⁻¹ and an RMSE of ±0.497 mm d⁻¹. The goodness of fit indicators showed a good agreement between the large and mini-lysimeter barley and potato ET_c measurements at daily time step. Single (K_c) and dual crop coefficients (K_cb, crop transpiration + K_e, soil evaporation) were derived from the lysimeter measurements, the grass reference evapotranspiration (ET_o) and the FAO56 dual K_c approach; after temperate standard climate adjustment, mid-season values were K_{c mid (std)} = 1.05 and K_{cb mid (std)} = 1.00 for barley; and K_{c mid (std)} = 1.06 and K_{cb mid (std)} = 1.02 for potato. The good agreement found between K_cb values and f_c will allow barley and potato water requirements to be accurately estimated. Full article