Antenna Gain Unit Converter (dBi dBd)
Antenna gain is quoted against one of two reference antennas.
Enter Values
How to use this calculator
- Enter your antenna's rated gain in EITHER the dBi field OR the dBd field — not both.
- Read off the converted value in the other unit, plus the linear gain factor over an isotropic radiator.
- Use dBi when comparing against isotropic references (Wi-Fi, cellular, link budgets) and dBd when comparing against dipole-referenced ham/broadcast antennas.
How it works
Antenna gain is quoted against one of two reference antennas. dBi is referenced to a theoretical isotropic radiator (equal power in all directions); dBd is referenced to a half-wave dipole. Because a lossless half-wave dipole itself has a gain of 2.15 dBi, the two scales differ by exactly that fixed offset: dBi = dBd + 2.15 and dBd = dBi − 2.15.
The tool also expresses the gain as a linear power ratio over isotropic using G = 10^(dBi ÷ 10). This turns the logarithmic decibel figure into a plain multiplier — for example 3 dBi ≈ 2× and 10 dBi = 10× the isotropic power density in the main lobe. All maths is a fixed offset plus a power-of-ten, so the result is exact for any input.
Worked example
Convert a 7 dBd antenna to dBi. A whip antenna is spec'd at 7 dBd. Enter 7 in the Gain (dBd) field. dBi = 7 + 2.15 = 9.15 dBi. Its linear gain over an isotropic radiator is 10^(9.15 ÷ 10) = 8.22×, meaning it concentrates power about 8.2 times more than an ideal isotropic antenna in its favoured direction.
Common mistakes
- Comparing a dBi antenna directly against a dBd antenna without converting — the same physical antenna reads 2.15 dB higher in dBi, so an unconverted comparison overstates the dipole-referenced one.
- Assuming the 2.15 dB offset applies to other references (e.g. dBiC or over a ground plane). It is specifically the isotropic-vs-half-wave-dipole difference.
- Treating the linear gain as a voltage ratio. 10^(dBi ÷ 10) is a POWER ratio; for a voltage/field ratio you would use 10^(dBi ÷ 20).
Frequently asked questions
Why is the difference between dBi and dBd exactly 2.15 dB?
A lossless half-wave dipole has a gain of 2.15 dBi relative to an isotropic radiator. Since dBd measures gain relative to that dipole, any gain figure is simply 2.15 dB lower in dBd than in dBi: dBi = dBd + 2.15.
Which unit should I use, dBi or dBd?
dBi is the more common modern standard and is used in Wi-Fi, cellular and RF link budgets. dBd is common in amateur radio and broadcast antenna specs. Convert everything to one reference before comparing antennas or building a link budget.
Does this account for cable loss or transmit power?
No. This converts only the antenna's gain figure between reference units. For end-to-end signal strength, combine the gain with transmit power, feedline loss and path loss using the related RF tools.
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Tip: Enter any known values to calculate the remaining results.
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