PET (aka ETo) is short for “Potential Evapotranspiration”. This is the measurement of the total amount of water that a plant needs to grow.
Tc is the turf coefficient for a specific grass. In other words, it is the water requirement for the specific type of grass calculated as a fraction of the PET.
Qf is the quality factor. This is a fraction of the PET used to maintain a certain grass quality. In residential applications, you are looking for the lawn to show a good appearance. That can be achieved without reaching full growth potential.
The figures we provide apply to Texas. Please visit TexasET network to learn more of how these figures are calculated, what assumptions are made, and what methodology is used to come up with these values.