Watt to dBi Calculator

This tool converts transmitter output power and Effective Isotropic Radiated Power (EIRP) in Watt to Antenna gain in dBi.

It calculates the Gain required to hit the target EIRP.

dBi to Watt Calculator


GAnt  = EIRP + LC – PTx


An antenna’s dBi value is a measure of its gain compared to a reference antenna. The reference antenna is isotropic, which means that it emits signal equally in all directions. An antenna with a higher dBi value has more gain than an antenna with a lower dBi value.

dB values are always relative to something else – in this case, relative to an isotropic antenna.

When choosing an antenna for a particular application, it is important to consider its gain. A directional antenna with high gain can be a good choice for applications where you need to maximize the signal strength in a specific direction, such as when aiming a radio signal at a specific target. However, directional antennas can also make it more difficult to receive signals from other directions, so they are not always the best choice for every application.

Antennas for cell phone boosters and TVs are often directional to maximize signal from a fixed cell tower or TV station. Antennas in your cell phone on the other hand, are omni-directional as the signal can be received from any direction.

Example Calculation

If the output power from a transmitter is 1 Watt, and the target EIRP is +33 dBm or 2 Watt, an antenna gain of 3 dBi is required. This assumes no cable loss.

Wideband Directional Antenna 700-2700 MHz,11 dBi Yagi High Gain 3G/4G/ LTE/Wi-Fi Universal Fixed Mount Directional Antenna for Wilson Cellphone Amplifier/Cellular Signalbooster with N Female Connector
11 dBi Directional Antenna