# dBi to dBm Calculator

Use this calculator to find the maximum output power of a transmitter in dBm. Enter:

• Antenna gain (dBi)
• Cable Loss (dB)
• Effective Isotropic Radiated Power (EIRP)

dBm to dBi

## Formula

PTx = EIRP + LC – GAnt

The maximum EIRP for a LoRa device operating at 922 MHz in Japan is +27 dBm. Let’s say the maximum antenna gain is specified to be 2 dBi.

Using these numbers and a cable loss of 1 dB, the maximum output power from the transmitter is restricted to 26 dBm.

## Background

An antenna’s dBi value is a measure of its gain compared to a an isotropic antenna. Isotropic antennas radiate signal equally in all directions. An antenna with a higher dBi value has more gain than an antenna with a lower dBi value.

Antenna gain can be calculated from Antenna Factor and Frequency.

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.