dBd to dBi Calculator

This handy tool converts antenna gain from deciBel relative to a dipole (dBd) to deciBel relative to an isotropic antenna (dBi).

Calculator

Enter the dBd value and the tool will compute the dBi gain value.

ðŸ”„ dBi to dBd

Formula

Gain (dBi) = Gain (dBd) + 2.15

Background

The terms dBi and dBd are used to describe the gain of an antenna compared to a reference. They are both units of measure to express the gain, but they use different references.

dBi – what does it mean?

dBi stands for decibels relative to an isotropic radiator. An isotropic radiator is a theoretical point source of electromagnetic waves that radiates the same intensity of radiation in all directions. It has no physical form but serves as a useful comparison standard.

When the gain of an antenna is given in dBi, it means the gain is compared to the isotropic radiator. A higher dBi value indicates a stronger antenna that can send or receive signals more effectively over distance.

The picture below shows how higher dBi antennas focus energy and transmit over longer ranges.

dBd – what does it mean?

dBd stands for decibels relative to a dipole antenna. A dipole antenna is a real, practical antenna that consists of two identical conductive elements such as metal wires or rods with a gap in between. The elements transmit or receive electromagnetic energy.

The gain of an antenna in dBd is its gain compared with the gain of a half-wave dipole antenna. Since a half-wave dipole antenna has a gain of 2.15 dBi, there’s a fixed relationship between dBi and dBd:

Gain (dBi) = Gain (dBd) + 2.15

An antenna’s gain in dBd is always 2.15 dB less than its gain in dBi because an isotropic radiator is considered to have a uniformly distributed radiation pattern, whereas a dipole has a directional pattern.