Free-space path loss
Calculate the ideal free-space loss from frequency and distance.
Free-space path loss
60.23 dB
Subtract this loss in a link budget. Antenna gains and other losses are separate terms.
- Free-space wavelength
- 122.36 mm
- Separation / wavelength
- 81.72 λ
Power ratios
- Loss factor · Pt/Pr
- 1.05 times ten to the power 6
- Received fraction · Pr/Pt
- 9.48 times ten to the power -7
Pt is transmitted power; Pr is received available power for matched, polarization-aligned isotropic antennas in the far field.
How the loss changes
- Double the distance · 20 m
- 66.25 dB
Frequency stays fixed.
- Double the frequency · 4.9 GHz
- 66.25 dB
Distance stays fixed.
Either change adds 6.02 dB to the isotropic reference loss.
Free-space reference. Assumes an unobstructed far-field path. Antenna dimensions also determine the required separation; distance in wavelengths alone cannot confirm it. Walls, reflections, fading and atmospheric attenuation are not calculated.
Model & assumptions
Free-space path loss compares transmitted power with available received power between isotropic reference antennas. For separation and free-space wavelength in the same units, the loss in dB is:
Wavelength is , where is frequency in hertz and is 299,792,458 m/s. The loss describes geometric spreading, rather than power absorbed by space. Doubling distance or frequency adds approximately 6.02 dB.
This model assumes an unobstructed far-field path and matched polarization. Antenna dimensions as well as wavelength determine the far field. Antenna gains, feeder losses, polarization mismatch, atmosphere, obstructions and fading belong elsewhere in the link budget. Free-space loss alone does not establish usable radio range.
For example, at 2.45 GHz a 10 m free-space path has approximately 60.23 dB loss.
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