ERP / EIRP Calculator

ERP (Effective Radiated Power) is how much power your antenna system radiates compared to a half-wave dipole. The FCC limits some bands by ERP, not transmitter output. A high-gain antenna could put you over the legal limit even at low TX power. On 60 meters, for example, 100 W into a 3-element Yagi would be roughly 560 W ERP — well over the 100 W ERP channel limit.

ERP references a half-wave dipole (gain in dBd). EIRP references a theoretical isotropic radiator (gain in dBi). EIRP is always 2.15 dB higher than ERP (that's 1.64x in watts). The FCC uses ERP for 60m and EIRP for 2200m, 630m, and 4mm. This calculator shows both so you can check either limit.

Effective February 13, 2026: amateurs get 4 discrete channels at 100 W ERP max, plus a new 15 kHz segment (5351.5–5366.5 kHz) at 9.15 W ERP max (equivalent to 15 W EIRP per WRC-15). Channel 3 (5368 kHz) was removed to protect NTIA operations. With a dipole (0 dBd), set your radio to 100 W on channels or ~9 W on the segment. Higher-gain antennas require lower TX power to stay legal.

No. Most HF, VHF, and UHF bands limit your transmitter's PEP output (1,500 W max), not the radiated power. You can use any antenna gain you want. ERP/EIRP limits only apply on 60m, 630m, 2200m, 70cm satellite uplink, and 4mm.

Use our Coax Loss Calculator — enter your cable type, length, and frequency to get the dB loss. Or measure it directly with an antenna analyzer at your operating frequency. Typical values: 50 ft of RG-8X at 5 MHz = ~0.6 dB; 100 ft of LMR-400 at 5 MHz = ~0.4 dB.

dBd = dBi − 2.15. A "5 dBi" antenna is 2.85 dBd. A "7.5 dBd" Yagi is 9.65 dBi. This calculator handles the conversion automatically — select your gain unit (dBd or dBi) and it figures out the rest.