EIRP / ERP Calculator
Calculate effective radiated power from transmitter power, feedline loss, antenna gain and efficiency.
Keep EIRP and ERP conventions straight
EIRP and ERP are measures of effective radiated power that combine transmitter power, feedline losses and antenna gain. The reference for ERP is dBd, while EIRP uses dBi, so mixing those gain references produces a systematic error.
Use measured or documented feedline loss where possible. Connector losses are normally small in a short installation but can become relevant when several adapters, relays or long cable runs are involved.
Treat the result as an engineering estimate and check the applicable national rules before transmitting. Regulatory power limits can depend on more than a simple EIRP number.
Use the result when checking station power
EIRP and ERP describe radiated power after antenna gain and, depending on the reference, feedline loss are considered. The distinction matters because ERP uses a half-wave dipole as the reference while EIRP uses an isotropic radiator. The two values therefore differ by about 2.15 dB when the same gain is expressed against those references. When checking a station, keep the power definition consistent: transmitter output, power at the antenna terminals, and radiated equivalent power are not interchangeable. Feedline loss reduces the power delivered to the antenna, while antenna gain changes the effective radiated value. The calculator is useful for estimating these relationships and for spotting unit or reference mistakes in equipment specifications. Regulatory limits vary by country and service, so an EIRP or ERP result should not be treated as a statement of legal compliance. Where compliance matters, use the applicable regulator's current rules and the manufacturer's verified data.