dBi Calculator

dBi stands for deciBel isotropic [1]. It is the gain of an antenna relative to that of a theoretical isotropic antenna [2].

An Isotropic antenna radiates energy equally in all directions. By contrast a directional antenna focuses energy in a particular direction. The higher the dBi value, the more focused the antenna beam.

Use this Calculator to find the Antenna dBi Gain using:

dBi Formula

Gain (dBi) = 20*Log10(9.73/[λ*(10)AF/20])


  • λ = Wavelength = c/f, where c is the speed of light and f is the frequency
  • AF = Antenna Factor

Note that dBi represents a ratio and not an absolute quantity.

Related Calculators

Use our

  • dBi to dBm converter to calculate the maximum transmit power for a specified EIRP (Effective Isotropic Radiated Power)
  • dBm to dBi converter to determine the maximum antenna gain such that the EIRP doesn’t exceed the FCC specified limit.


The higher the dBi, the more focused the energy and the higher the antenna gain.

Helium hotspot owners use high gain antennas to focus in a direction with larger numbers of witnesses. The highest gain we’ve seen in practical use is 8 dBi.

Antenna Gain

Many TV antennas are of the directional Yagi-Uda type (shown in the picture below) and can be pointed in the direction of the transmitting tower for better signal reception.

Yagi-Uda antenna by Tennen-Gas


[1] DeciBel Antenna Measurements on Wikipedia

[2] Isotropic Radiator on Wikipedia