EIRP Calculator
Radiated Power & Path Loss

EIRP stands for Effective Isotropic Radiated Power. It is the hypothetical power that an isotropic antenna (one that radiates equally in all directions) would need to emit to produce the same peak power density in the direction of maximum antenna gain. EIRP combines the transmitter output power, antenna gain, and cable/connector losses into a single figure that represents the effective strength of a wireless transmission.

EIRP (Effective Isotropic Radiated Power) is referenced to a perfect isotropic antenna (0 dBi gain). ERP (Effective Radiated Power) is referenced to a half-wave dipole antenna, which has a gain of 2.15 dBi over an isotropic radiator. Therefore, ERP = EIRP − 2.15 dBi. Both measure radiated power, but use different reference antennas. Most regulatory bodies (FCC, ETSI) specify limits in EIRP.

EIRP (dBm) = Transmit Power (dBm) + Antenna Gain (dBi) − Cable & Connector Losses (dB). First, convert transmit power to dBm if needed: dBm = 10 × log10(Power in Watts × 1000). Then add antenna gain and subtract all losses in the transmission line. Example: 20 dBm Tx power + 6 dBi antenna gain − 1.5 dB cable loss = 24.5 dBm EIRP = approximately 282 mW.

FCC EIRP limits vary by frequency band and use case. Common limits include: Wi-Fi 2.4 GHz (802.11b/g/n) indoors: 36 dBm (4 W) under Part 15.247; Wi-Fi 5 GHz (802.11a/n/ac) indoors: 30 dBm (1 W) under Part 15.407; Wi-Fi 6 GHz (802.11ax): 30 dBm indoor, 24 dBm outdoor; Bluetooth 2.4 GHz: 20 dBm (100 mW) under Part 15. Point-to-point links at 5 GHz can exceed these limits if antenna gain increases are offset by reduced transmitter power. Always consult the applicable regulations for your jurisdiction.

EIRP is fundamental to wireless network design for two reasons. First, regulatory compliance: radio regulatory bodies like the FCC, ETSI, and ISED set maximum EIRP limits for each frequency band to prevent interference between wireless systems. Exceeding these limits can result in fines or equipment seizure. Second, link budget planning: EIRP directly determines the coverage area of a wireless system. Combined with free-space path loss, receiver sensitivity, and antenna gain, EIRP allows engineers to predict signal strength at any distance and ensure reliable connections.