In radio transmission, transmitter power output (TPO) is the actual amount of power (in watts) of radio frequency (RF) energy that a transmitter produces at its output.

TPO is a concept related to effective radiated power (ERP), but refers to the power output of a transmitter, without accounting for antenna gain. The ERP for VHF/UHF transmitters is normally more than the TPO, for LF/MF transmitters it has nearly the same value, while for VLF transmitters it may be less.^{[clarification needed]}

The radio antenna's design focuses the signal, creating gain and increasing the ERP. There is also some loss (negative gain) from the feedline, which reduces some of the TPO to the antenna by both resistance and by radiating a small part of the signal.

The basic equation relating transmitter to effective power is:

Note that in this formula the Antenna Gain is expressed with reference to a dipole (dBd)