ConverterHub

Gain (dBi) to Gain (dBd) Converter

Enter a value in gain (dbi) to convert it to gain (dbd).

How it is calculated

The conversion is a fixed subtraction: dBd = dBi − 2.15. Both units are decibels, so no multiplication is involved. The offset exists because a half-wave dipole already has about 2.15 dB more gain than an isotropic radiator, so the same antenna reads 2.15 lower when measured against the dipole. The input is any number (negative values work too) and the result is rounded to two decimals with the dBd label. To go the other way, add 2.15 to a dBd figure. The tool does not convert to linear power ratios.

Worked example

A panel antenna is rated 9 dBi. Subtract the dipole offset: 9 − 2.15 = 6.85. The tool displays 6.85 dBd. So the same antenna has 6.85 dB of gain over a half-wave dipole, which is a power ratio smaller than the 9 dB compared to an ideal isotropic source.

Try this example →

Common mistakes

  • Adding 2.15 instead of subtracting it when going from dBi to dBd; the dBd number is always the smaller one.
  • Comparing a dBi datasheet value with a dBd value from another vendor without converting one of them first.
  • Confusing dBd with dBm or dBW; dBi and dBd describe gain relative to an antenna, not absolute power.
  • Expecting the result to be a linear multiplier; the figure stays in decibels and values add or subtract rather than multiply.

About this calculator

Antenna gain can be quoted against two different reference antennas: dBi compares against a theoretical isotropic radiator (equal energy in all directions), while dBd compares against a real-world half-wave dipole, which itself has 2.15 dB of gain over an isotropic source. That fixed offset gives the conversion: dBd = dBi − 2.15 dB (and dBi = dBd + 2.15 dB).

RF and antenna engineers need to convert between the two constantly because manufacturers aren't consistent — WiFi and cellular antenna datasheets often quote dBi, while some amateur radio and broadcast antenna specs use dBd — and comparing two antennas' gain figures without converting them to the same reference can make one antenna look better than it actually is.

Was this helpful?

You can pick up to 3 reactions.

Be the first to comment.

Popular calculators

Loan Calculator

Monthly payment, total interest and full amortization schedule.

Percentage Calculator

Percent change, percent of, and ratio calculations.

Discount Calculator

Calculate final price, savings, and discount amount.

BMI Calculator

Body mass index from height and weight (metric or imperial).

Age Calculator

Compute your exact age in years, months and days from a birth date.

Compound Interest Calculator

Calculate the final amount and interest earned with compounding.

All Calculators