Effective Isotropic Radiated Power

EIRP = Ptx + Gant − L_cable (dB)

Calculator

Result
—

Formula

EIRP(dBm) = P_tx(dBm) + G_ant(dBi) − L_cable(dB)

Description

Effective Isotropic Radiated Power (EIRP) is the total power that would need to be radiated by an isotropic antenna to produce the same signal strength in the direction of maximum antenna gain. It accounts for the transmitter output power, the antenna gain (which concentrates energy in preferred directions), and the cable losses between the transmitter and antenna. EIRP is the key parameter for link budget calculations, regulatory compliance, and interference analysis. Amateur radio and ISM band regulations often specify maximum EIRP limits.

Variables

  • EIRP — Effective isotropic radiated power (dBm)
  • P_tx — Transmitter output power (dBm)
  • G_ant — Antenna gain relative to isotropic (dBi)
  • L_cable — Total feed line loss (dB)

Practical Notes

FCC Part 97 limits amateur radio EIRP to 1500W PEP (about 61.8 dBm) on most bands. ISM devices under Part 15 are limited to much lower EIRP. To convert watts to dBm: P_dBm = 10×log₁₀(P_watts) + 30. A 100W transmitter (50 dBm) with a 10 dBi antenna and 2 dB cable loss produces 58 dBm EIRP (631W equivalent).

Related Formulas

Quarter-Wave Antenna Length Half-Wave Dipole Length Coaxial Stub Length (λ/4) SWR Reflected Power Antenna Beamwidth

Need more features?

Save calculations, import telemetry data, simulate battery discharge, and collaborate with your team.

Try the App