The Transpiration Coefficient (TK) indicates how many liters of water a plant transpires (must transpire) to produce one kilogram of dry matter. For most horticultural crops, the TK ranges between 400 and 600, while for efficient plants such as maize, it is around 300-400.

The TK can be used to compare the water use efficiency (WUE) of different plants, cultivation methods, etc. Furthermore, it helps estimate whether the supply of nutrient elements via the water stream would be sufficient to adequately nourish the plant (see lecture: Transport Processes, Mass Flow)