Effective Isotropic Radiated Power (EIRP) is the equivalent power that an isotropic (omnidirectional) antenna would need to radiate to produce the same peak signal strength in a given direction as the actual transmit system. It is the standard power metric for regulatory compliance and link budget analysis.

What is the EIRP formula?

EIRP (dBm) = Transmit Power (dBm) − Cable & Connector Losses (dB) + Antenna Gain (dBi). When antenna gain is given in dBd (relative to a dipole), add 2.15 dB to convert to dBi first, since a dipole has 2.15 dBi gain over an isotropic radiator.

What is the difference between dBi and dBd?

dBi expresses antenna gain relative to a theoretical isotropic radiator (equal power in all directions). dBd expresses gain relative to a half-wave dipole antenna, which itself has 2.15 dBi gain. Therefore: Gain (dBi) = Gain (dBd) + 2.15 dB. Most regulatory limits are stated in dBm EIRP using dBi gain.

What are typical EIRP regulatory limits?

Common limits include: Wi-Fi 2.4 GHz (ISM) — 30 dBm EIRP in many regions; Wi-Fi 5 GHz U-NII-1 — 23 dBm EIRP (FCC indoor); Wi-Fi 5 GHz U-NII-3 — 30 dBm EIRP; 900 MHz ISM LoRa — 30 dBm EIRP in the US. Always confirm with the applicable regional regulatory body.

How do I convert between dBm and watts?

Power (W) = 10^((dBm − 30) / 10). For example, 30 dBm = 1 W, 20 dBm = 100 mW, 10 dBm = 10 mW, 0 dBm = 1 mW. This calculator shows the conversion automatically for every result.

Should I include connector losses in cable loss?

Yes. The "cable loss" field should include all insertion losses between the transmitter output and the antenna feed point: coaxial cable, RF connectors, adapters, filters, duplexers, and lightning arrestors. Each component is typically listed in its datasheet as an insertion loss in dB.

EIRP Calculator

Enter transmit power, cable/connector losses, and antenna gain to instantly compute EIRP in dBm and watts.

Transmitter Parameters

Transmit Power

Cable & Connector Loss

Include all cable, connector, and filter losses between TX output and antenna feed point.

Antenna Gain

dBd values are automatically converted to dBi (+2.15 dB).

Quick Presets

EIRP Formula

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

Note: dBd gain is converted to dBi by adding 2.15 dB.

Formula Breakdown

Parameter	Value	Note

Regulatory Limits Reference

Band / Standard	Max EIRP	Status

Fill in the transmitter parameters, then click Calculate EIRP.

Summary

Effective Isotropic Radiated Power (EIRP) is the total power a transmitter system appears to radiate in a given direction, referenced to an isotropic antenna. It combines the transmitter output power, any cable or connector losses, and the antenna gain into a single figure — EIRP (dBm) = P_tx (dBm) − Cable Loss (dB) + Antenna Gain (dBi). EIRP is a fundamental metric in RF link budgets, regulatory compliance (FCC, ETSI), and coverage planning for Wi-Fi, cellular, satellite, and other wireless systems.

How it works

Enter the transmitter output power in dBm or watts.
Enter all cable, connector, and filter losses in dB (combined or per component).
Enter the antenna gain in dBi (referenced to an isotropic radiator) or dBd (referenced to a dipole).
Click Calculate to apply EIRP = P_tx − Losses + Gain.
Review the result in dBm, watts, and milliwatts, along with a formula breakdown.
Use the preset buttons for common wireless standards to quickly explore typical values.

Use cases

Verifying FCC or ETSI EIRP limits for Wi-Fi, cellular, and licensed radio links.
RF link budget analysis — establishing the transmit side of the power budget.
Comparing antenna systems by computing the net radiated power.
Satellite uplink and downlink design — ensuring regulatory EIRP compliance.
Amateur radio (ham) station power planning on VHF, UHF, and microwave bands.
Fixed wireless and point-to-point backhaul link engineering.
Drone and UAV command-and-control link power planning.
IoT and LoRa deployment power budgeting for outdoor range estimation.

Frequently Asked Questions

Last updated: 2026-05-23 · Reviewed by Nham Vu