Lysimeters are basic instruments for evapotranspiration measurement. This study characterized the actual evapotranspiration of unirrigated and unfertilized grass in a warm region of the Czech Republic on a Chernozem loamy soil. An SFL-300 weighing lysimeter (diameter 0.3 m, depth 0.3 m) was used for this purpose. The suction at its bottom was maintained at the same level as in the native soil nearby. We selected 585 rainless days with regular records for the analysis of daily differences. On most days, the lysimeter-measured actual evapotranspiration, ET a , was smaller than the Penman-Monteith FAO 56 reference crop evapotranspiration, ET 0 . The FAO 56 procedure was found to be a reasonable estimator of the unstressed evapotranspiration in a moderately stressed environment. The ET a /ET 0 ratio and the canopy surface resistance, r s , depend on the soil water content and suction measured at 5 cm. These graphs break down into horizontal unstressed parts and declining (for ET a /ET 0 ) or inclining (for r s ) water-stressed parts. The ratio ET a /ET 0 is about 85% and r s is about 250 s m −1 when the grass is not under water stress. The annual curve of the unstressed crop coefficient has a sine shape. An energy balance criterion suggests that advection of heat is important in winter but not so much in summer. The study provides parameters of evapotranspiration for a canopy that can be found on many standard weather stations and demonstrates that high-quality research into evapotranspiration of low, dense, and shallow-rooting crops is possible with small lysimeters of this type.Abbreviations: ASCE, American Society of Civil Engineers; DOY, day of the year; ET, evapotranspiration; ET a , actual evapotranspiration; ET 0 , reference crop evapotranspiration; LYW, lysimeter weight (actually mass); SFL, smart field lysimeter; SWW, percolate collecting bottle mass.Evapotranspiration is a basic component of the natural water cycle and water balance. Its quantification is therefore of utmost importance for many branches of water management. The potential evapotranspiration, representing the climatic "demand" for water (Hillel, 1998;Irmak and Haman, 2003;Verstraeten et al., 2008) has long ago been recognized as a suitable benchmark to which other types of evaporation in nature can be related. The FAO 24 (Doorenbos and Pruitt 1977) and then the FAO 56 (Allen et al., 1998) and American Society of Civil Engineers (ASCE) (Jensen and Allen, 2016) methodologies offered a concept of the reference crop evapotranspiration, ET 0 , corresponding to the actual evapotranspiration of a standard, dense, and extensive herbal stand sufficiently supplied with soil water (and thus its potential evapotranspiration). The FAO 56 reference low crop is grass, assumed to be 0.12 m high, having a shortwave albedo of 0.23 and surface resistance of 70 s m −1 . Up to now, one of the widely used way of estimating ET 0 has been the one based on the Penman combination concept resulting in the PenmanMonteith evaporation equation (cf. Allen et al., 1998; f...