RF · radiated power
EIRP calculator.
Effective isotropic radiated power from your transmitter, cable loss and antenna gain.
Inputs
Radiated power
Enter values to calculate.
How do I calculate EIRP?
EIRP is the power an ideal isotropic antenna would need to radiate to match the peak of your antenna: EIRP (dBm) = transmitter power (dBm) - cable loss (dB) + antenna gain (dBi). An antenna gain quoted in dBd is relative to a half-wave dipole, and 0 dBd = 2.15 dBi, so add 2.15 to convert. ERP uses the dipole as the reference, which makes it 2.15 dB lower than EIRP.
Worked example. 20 dBm transmitter, 2 dB of cable loss and an 8 dBi antenna give 26 dBm EIRP, which is 398 mW, or 23.85 dBm ERP.
Regulators set limits on EIRP or ERP that depend on country, band and use. This tool does not state those limits; look up the current rule from your regulator, such as the FCC or ISED, before you transmit.
Frequently asked questions
What is the difference between EIRP and ERP?
EIRP is referenced to an isotropic antenna and ERP to a half-wave dipole. EIRP is 2.15 dB higher than ERP.
How do I convert dBd to dBi?
Add 2.15 dB.
Does cable loss reduce EIRP?
Yes. Loss between the transmitter and the antenna is subtracted.
What is the legal EIRP limit?
It depends on the country, band and device type. Check your regulator; this page does not set a limit.
Sources
Checked
EIRP and dBd/dBi relationships only; no regulatory limits are used. Runs entirely in your browser. Nothing you type is sent or stored.
Scope
Arithmetic only. Not a compliance determination; check your regulator for current limits.