Antenna Gain & Range Calculator
Convert antenna gain in dBi to a linear gain, EIRP and the theoretical range improvement over an isotropic antenna.
How it works
Linear gain = 10^(dBi ÷ 10) · Range multiplier = 10^(dBi ÷ 20) · EIRP(dBm) = Tx power + gain
Antenna gain does not create power — it concentrates the transmitter output into a narrower beam, so the peak signal is stronger in that direction. Because free-space received power falls with the square of distance, a gain that multiplies power by G lets the same signal reach √G times farther, which is why the range multiplier uses ÷20 instead of ÷10. EIRP adds the transmitter power and the antenna gain to give the effective radiated power a regulator cares about.
Worked example
A 9 dBi antenna has a linear gain of 10^(9 ÷ 10) = 7.9×, so it reaches 10^(9 ÷ 20) = 2.8× as far as an isotropic antenna. Fed with 20 dBm (0.1 W), its EIRP is 20 + 9 = 29 dBm, about 0.79 W.
Frequently asked questions
What is the difference between dBi and dBd?
dBi is referenced to a theoretical isotropic radiator; dBd is referenced to a half-wave dipole. A dipole already has 2.15 dBi of gain, so dBi = dBd + 2.15.
Does a higher-gain antenna really increase range?
Yes, but only in the direction the beam points — gain narrows the pattern, so a high-gain antenna trades wide coverage for reach. Pointing matters: a 12 dBi panel aimed away from the receiver helps nothing.
Why is EIRP regulated?
Regulators limit EIRP, not just transmitter power, because a big antenna on a modest transmitter can radiate as strongly as a powerful one on a plain antenna. Keeping EIRP within limits controls interference between users.
Related calculators
This calculator is for educational purposes. Double-check important results before acting on them.