Use this calculator to estimate free-space path loss in dB for quick RF and wireless planning checks.
Inputs
This topic also has a deeper guide and a printable reference pack, so you can move from the live answer into the method, assumptions, and worked examples without leaving the topic cluster.
A practical guide to free-space path loss, wavelength-aware intuition, and feedline loss, built to explain what the loss figure really means before you roll it into a larger RF or microwave link budget.
A practical guide to RF link budgets and received power that treats every gain and loss term as an accounting decision, making it easier to see whether a link is viable and where the margin is being won or lost.
These are the main values the calculator uses. Keep the units consistent and, where relevant, match the assumptions explained in the related guide.
Unit: km
Enter the line-of-sight path length in kilometres to match the formula form used here.
Unit: MHz
Use the operating frequency in megahertz so the path-loss constant stays valid.
Use this page when you want a quick free-space propagation loss estimate before building a wider wireless or RF link budget.
The main result is free-space path loss in dB. The supporting value repeats the entered distance so the unit basis stays obvious.
At a higher frequency or longer distance, the path loss rises. That is why long microwave links and high-frequency systems need careful gain and loss budgeting.
This is a free-space model only. It does not include terrain, foliage, diffraction, polarisation mismatch, weather fade, or implementation losses.
No. It is a useful baseline, but real links also need antenna gains, feeder losses, receiver sensitivity, fade margin, and local propagation effects.
Combine transmitter power, antenna gains, path loss, and miscellaneous losses to estimate received power.
Estimate received power from transmitter power, antenna gains, distance, and frequency using the free-space Friis relationship.
Use the Wavelength from Frequency Calculator for quick wavelength from frequency estimates in RF, radar, and communications work.
Estimate the line-of-sight radar horizon from antenna height and target height using a standard engineering approximation.