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ERP / EIRP Calculator

Calculate effective radiated power from transmitter output, feedline and connector losses, and antenna gain. Enter gain in either dBi or dBd and the calculator will show both ERP and EIRP.

System inputs

Power available at the transmitter output connector before feedline losses.
Total coax/feedline attenuation between transmitter and antenna.
Optional additional loss for connectors, filters, duplexers, combiners or other passive components.
dBi is referenced to an isotropic radiator; dBd is referenced to a half-wave dipole.
RF power through the system Live calculation

Enter transmitter power to see where power is lost and how antenna gain changes the final ERP and EIRP.

How the calculation works

Start with the transmitter output power in logarithmic form, subtract all RF losses between the transmitter and antenna, then add the antenna gain.

EIRP (dBW) = TX power (dBW) − losses (dB) + antenna gain (dBi)
ERP (dBW) = TX power (dBW) − losses (dB) + antenna gain (dBd)

The two antenna-gain references differ by 2.15 dB:

Gain (dBi) = Gain (dBd) + 2.15
EIRP (dBW) = ERP (dBW) + 2.15

Worked example

Enter transmitter power above to see the calculation worked through here.

Power at the antenna input

Feedline and connector losses reduce the RF power that physically reaches the antenna. If the total system loss is 2 dB, the antenna receives about 63% of the transmitter power.

ERP versus EIRP

ERP is referenced to an ideal half-wave dipole. EIRP is referenced to an isotropic radiator. For the same physical system, EIRP is 2.15 dB higher than ERP.

Why both results are shown

Technical specifications, licence conditions and equipment documents may use either ERP or EIRP. Always check which reference is actually required before comparing a calculated result with a limit or specification.

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