RF Engineering
What Is EIRP? EIRP vs ERP and How to Calculate It
EIRP is the power a perfect isotropic antenna would have to radiate to match what your real antenna sends along its main beam. You get it by adding the transmitter power and the antenna gain, then subtracting the feeder loss. Here is the formula, how EIRP differs from ERP, a worked example, and the licence limits and safety distances that all depend on it.