What is free-space path loss?

FSPL is how much a radio signal weakens as it spreads out over distance in empty space, with clear line of sight and no obstacles. It is the theoretical best case; real links always lose more.

How is FSPL calculated?

FSPL(dB) = 20·log10(d) + 20·log10(f) + 20·log10(4π/c). With distance in metres and frequency in Hz this is 20·log10(d) + 20·log10(f) − 147.55. Equivalently, in km and GHz: 92.45 + 20·log10(d_km) + 20·log10(f_GHz).

Why does higher frequency mean more loss?

Higher-frequency antennas capture energy over a smaller effective area (aperture shrinks with λ²), so for the same physical link the received power drops. Doubling frequency adds 6 dB of path loss.

What is a link budget?

A link budget adds up all the gains and losses between transmitter and receiver. Here: received power = transmit power + transmit gain + receive gain − path loss. Cable losses and noise are not included.

Free-Space Path Loss (FSPL) Calculator

Free FSPL calculator. Enter frequency and distance to get free-space path loss in dB, plus an instant link budget (EIRP and received power) from transmit power and antenna gains. Based on the Friis equation and ITU-R P.525.

Compute radio path loss and a simple link budget from frequency and distance.