Antenna Gain Converter
Enter a gain in dBi, dBd, or as a linear ratio and read it back in all three, plus an estimated half-power beamwidth for a symmetric beam.
Compare antennas on equal terms
Two antennas can look very different on paper simply because one is quoted in dBi and the other in dBd. Put both on the same scale and the comparison becomes honest — a 12 dBi panel and a 10 dBd panel are the same antenna. The beamwidth estimate then tells you how tightly that gain is focused, which decides how carefully the link has to be aimed.
Drop the converted gain straight into the RF Link Budget Calculator, check how much loss the antennas have to overcome with the Free-Space Path Loss Calculator, and cut elements to the band with the Frequency & Wavelength Calculator.
Frequently Asked Questions
What is the difference between dBi and dBd?
Both express antenna gain, but against different references. dBi is gain over an isotropic radiator — a theoretical point that radiates equally in every direction. dBd is gain over a half-wave dipole. Because a dipole itself has 2.15 dBi of gain, the two scales differ by exactly that: dBd = dBi − 2.15. Manufacturers quote whichever looks better, so converting before you compare two antennas stops you overstating one by 2.15 dB.
What does the linear ratio mean?
Gain in decibels is a logarithm of a power ratio, so 'linear' is that raw ratio: linear = 10^(dBi/10). A 3 dBi antenna concentrates about twice the power of isotropic in its main direction, 10 dBi about ten times, 20 dBi about a hundred. The linear form is handy when you multiply gains and losses directly rather than adding decibels.
How is beamwidth related to gain?
A higher-gain antenna focuses energy into a narrower beam, so gain and beamwidth are two views of the same thing. This tool uses the standard Kraus approximation for an ideal symmetric pencil beam, gain ≈ 41253 / (θ_E · θ_H) square degrees, and solves it for a single half-power beamwidth. It is a first-order estimate: real antennas have sidelobes and asymmetric patterns, so measured beamwidth will differ.
Why does the estimated beamwidth not match my antenna's datasheet?
The 41253 formula assumes an ideal, loss-free, symmetric main beam and no sidelobes, and it collapses the two principal-plane beamwidths into one symmetric figure. Practical antennas radiate some power into sidelobes and often have different E- and H-plane beamwidths, so the true gain for a given beamwidth is a few dB lower. Use the estimate for a sanity check, and trust a measured pattern for the real figure.
Conversions are exact; the beamwidth is a first-order estimate for an ideal symmetric beam. Trust a measured antenna pattern for real figures. Not engineering advice.