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Free-Space Path Loss Calculator

Calculate ideal free-space propagation loss from frequency and distance, or work backwards from a known path-loss budget to determine the corresponding free-space distance.

Calculate

Carrier or centre frequency of the radio link.
Straight-line separation between the two antennas.
Optional; used only for the ideal received-power estimate.
Free-space RF linkIdealised

Enter frequency and distance to visualise the ideal free-space link.

How the calculation works

Free-space path loss is the reduction in power density caused purely by geometric spreading of an electromagnetic wave in unobstructed free space.

FSPL (dB) = 20 log10(d) + 20 log10(f) + 32.44

Here d is in kilometres and f is in megahertz.

FSPL = 20 log10(4πd / λ)

Worked example

Enter values above to see the calculation worked through here.

Optional received-power estimate

PRX (dBm) = PTX (dBm) + GTX + GRX − FSPL

If transmitter power and antenna gains are entered, the calculator applies this ideal Friis link-budget relationship.

What FSPL does not include

This is an ideal propagation model. Real terrestrial links may experience additional loss or gain from terrain, antenna height, diffraction, reflections, foliage, buildings, atmospheric effects and multipath.