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Free Space Path Loss Calculator

Enter the distance in km and frequency in MHz to get the free-space path loss in dB.

How to use

  1. Enter your values in the fields above.
  2. Press Calculate to see your result instantly.
  3. Use the Share button to copy a link to your result.

About this calculator

This calculator applies the standard Free-Space Path Loss (FSPL) formula: FSPL(dB) = 20·log₁₀(d) + 20·log₁₀(f) + 32.44, with distance d in kilometres and frequency f in megahertz. It's derived from the Friis transmission equation and describes how much a radio signal weakens purely from spreading out over distance in open space, with no obstructions, reflections or atmospheric absorption.

RF engineers, wireless ISPs and radio amateurs use FSPL as the baseline term in a link budget — the calculation that adds transmitter power and antenna gains, then subtracts path loss and cable losses, to check whether a receiver will get enough signal. Doubling the distance or the frequency each adds about 6 dB of loss.

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