EIRP Calculator
Calculate Effective Isotropic Radiated Power (EIRP) with EIRP = Tx − Lc + Ga. Free online RF calculator with ERP, watt conversion, charts, and step-by-step breakdown.
About This Calculator
The EIRP Calculator helps RF engineers, ham radio operators, and telecommunications professionals compute the Effective Isotropic Radiated Power of a transmitter-antenna system. EIRP is a critical parameter in link budget analysis, wireless network planning, and regulatory compliance with bodies like the FCC, ETSI, and WPC.
The calculation follows the standard formula: EIRP (dBm) = Transmitter Output Power (dBm) − Total Cable Loss (dB) + Antenna Gain (dBi). This accounts for the power output of your transmitter, all losses through cables and connectors, and the directional gain provided by your antenna. Understanding EIRP is essential when designing point-to-point microwave links, Wi-Fi deployments, cellular base stations, and satellite communication systems.
Our calculator also provides the ERP (Effective Radiated Power) — the equivalent power relative to a half-wave dipole antenna — using the standard conversion EIRP = ERP + 2.15 dB. Additionally, the output is converted to watts for intuitive understanding of the actual radiated power. Use the interactive bar and pie charts to visualize how each component (transmitter power, cable loss, and antenna gain) contributes to the final EIRP value.
Frequently Asked Questions
What is EIRP (Effective Isotropic Radiated Power)?
EIRP stands for Effective Isotropic Radiated Power — the amount of power a theoretical isotropic antenna would need to radiate to produce the same peak power density observed from the actual antenna system in its direction of maximum gain. It is widely used in RF engineering, telecommunications link budgets, and regulatory compliance.
What is the EIRP calculation formula?
The EIRP formula is: EIRP (dBm) = Transmitter Output Power (dBm) − Total Cable & Connector Losses (dB) + Antenna Gain (dBi). This accounts for the transmitter power, losses in cables and connectors, and the directional gain of the antenna.
What is the difference between EIRP and ERP?
EIRP uses an isotropic antenna (uniform radiation in all directions) as reference, while ERP (Effective Radiated Power) uses a half-wave dipole antenna. The conversion is: EIRP (dBm) = ERP (dBm) + 2.15. This means ERP is about 2.15 dB lower than EIRP for the same system. The gain units also differ: dBi for EIRP, dBd for ERP.
What is the FCC EIRP limit for Wi-Fi?
In the United States, the FCC limits point-to-multipoint systems in the 2.4 GHz band to 36 dBm (4 watts) EIRP. For point-to-point links operating under FCC Part 15.247, the limit increases by 1 dB for every 3 dB of antenna gain above 6 dBi, up to specified maximums. Always check current regulations for your specific use case.
How do I convert dBm to watts?
To convert from dBm to watts, use the formula: P(W) = 10^(P_dBm / 10) / 1000. For example: 30 dBm = 1 W, 0 dBm = 0.001 W (1 mW), 20 dBm = 0.1 W, and 10 dBm = 0.01 W. Our calculator performs this conversion automatically for the computed EIRP value.
Can I use this calculator for regulatory compliance?
Yes. This calculator helps you verify whether your system's EIRP falls within regulatory limits set by the FCC (United States), ETSI (Europe), WPC (India), or other bodies. However, for official compliance certification, you should always rely on calibrated measurement equipment and certified test reports.