MasterTool

Free Space Path Loss Calculator

Calculate free-space path loss for an RF link from frequency and distance.

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What this tool does

Calculate free-space path loss for an RF link from frequency and distance. Free-space line-of-sight only, with isotropic antennas. Obstruction, multipath, atmosphere and antenna gains belong in a full link budget, not in FSPL itself.

How to use the Free Space Path Loss Calculator

  1. Enter or select frequency (mhz).
  2. Enter or select distance (km).
  3. Read the calculated result; change any measurement to compare alternatives.

Formula

FSPL (dB) = 32.44 + 20log10(f MHz) + 20log10(d km)
frequency
Frequency (MHz)
distance
Distance (km)

Free-space line-of-sight only, with isotropic antennas. Obstruction, multipath, atmosphere and antenna gains belong in a full link budget, not in FSPL itself.

Worked example

For free space path loss calculator, the following measurements illustrate the exact method: Frequency (MHz): 2400; Distance (km): 1.

Inputs

  • Frequency (MHz)2400
  • Distance (km)1

Result

  • Free-space path loss (dB)100.04
  • Wavelength (m)0.12
  • Path loss at double the distance (dB)106.06

Results explained

Free-space path loss (dB)
Free-space path loss (dB) from the formula above. Free-space line-of-sight only, with isotropic antennas. Obstruction, multipath, atmosphere and antenna gains belong in a full link budget, not in FSPL itself.
Wavelength (m)
Wavelength (m) from the formula above. Free-space line-of-sight only, with isotropic antennas. Obstruction, multipath, atmosphere and antenna gains belong in a full link budget, not in FSPL itself.
Path loss at double the distance (dB)
Path loss at double the distance (dB) from the formula above. Free-space line-of-sight only, with isotropic antennas. Obstruction, multipath, atmosphere and antenna gains belong in a full link budget, not in FSPL itself.

Frequently asked questions

FSPL (dB) = 32.44 + 20·log₁₀(frequency in MHz) + 20·log₁₀(distance in km). At 2,400 MHz over 1 km that is 32.44 + 67.60 + 0 ≈ 100 dB.

The distance term is 20·log₁₀(d), so doubling d adds 20·log₁₀(2) ≈ 6.02 dB — the signal spreads over four times the area.

No. In a link budget you subtract FSPL from transmit power and add both antenna gains (in dBi) and subtract cable and other losses.

With clear line of sight and antennas in each other's far field, away from reflections and obstructions. Indoor or urban paths lose more — often much more — than FSPL.

For fixed (isotropic) antenna apertures the captured share of the spreading wavefront shrinks with wavelength; real antennas with fixed physical size partly offset this with higher gain.