tools / RF & SDR
EIRP and ERP Calculator
Add your antenna gain, subtract the cable loss, and this gives EIRP and ERP in dBm and watts. It is the figure regulators actually care about, and the one that decides whether your setup is legal on a given band.
ERP references a half-wave dipole, so it sits 2.15 dB below EIRP.
How it works
EIRP and ERP
EIRP (dBm) = TX power + antenna gain (dBi) minus feedline loss. ERP references a half-wave dipole instead of an isotropic radiator, so ERP is EIRP minus 2.15 dB.
FAQ
What is the difference between EIRP and ERP?
The reference antenna. EIRP compares to an ideal isotropic point source, ERP to a dipole. ERP is always 2.15 dB lower for the same setup.
How do antenna gain and cable loss change it?
Gain adds to radiated power one for one in dB, and cable loss subtracts. A high-gain antenna on a long lossy run can still come out ahead, but the loss is real power you paid for and never radiated.
