Free Space Path Loss Calculator

Work out free space path loss instantly with clear inputs, formula shown and shareable results.

About Free Space Path Loss Calculator

Free space path loss is 32.44 + 20log10(d in km) + 20log10(f in MHz) dB. Both distance and frequency contribute 6 dB per doubling, so a 5 GHz link loses 6 dB more than a 2.4 GHz one over the same distance. Antenna gain at each end is subtracted from that loss.

Formula

Free space path loss

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

Worked example

With the default values below, Free Space Path Loss Calculator returns Free space path loss of 114.02. Change any input above and every figure here is recalculated in your browser.

Inputs used

Distance: 5 km
Frequency: 2,400 MHz
Transmit antenna gain: 12 dBi
Receive antenna gain: 12 dBi

Results

Free space path loss: 114.02 dB
Net loss after antenna gains: 90.02 dB
Wavelength: 12.49 cm
First Fresnel zone radius at midpoint: 12.50 m

Step by step

1Values used
2Free space path loss
3Free space path loss= 114.02 dB
4Net loss after antenna gains= 90.02 dB
5Wavelength= 12.49 cm
6First Fresnel zone radius at midpoint= 12.50 m

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax or fees or charges into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why does higher frequency lose more?

The receiving antenna's effective aperture for a given gain shrinks with wavelength, so it intercepts less of the spreading wavefront.

What is the Fresnel zone for?

Obstacles intruding into the first Fresnel zone cause diffraction loss. Clearing 60% of its radius is the usual planning requirement.