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Free Space Path Loss Calculator
Calculate free-space path loss in dB from radio frequency and distance using the Friis transmission formula for link budgeting.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Free Space Path Loss (FSPL)
Net Path Loss (with Gains)
RF Wavelength (λ)
Speed of light c / f
How it works
- Enter the carrier transmission frequency (e.g. 2.4 GHz for Wi-Fi/Bluetooth or 5.8 GHz for FPV video links).
- Specify the distance between transmitter and receiver antennas in meters, kilometers, miles, or feet.
- Input transmitter (Tx) and receiver (Rx) antenna gains in dBi.
- The calculator computes the raw free space path loss in decibels (dB), net link attenuation, and exact RF wavelength.
The formula
FSPL (dB) = 20 × log₁₀(4πd / λ) = 20 log₁₀(d) + 20 log₁₀(f) + 32.45 (for d in km, f in MHz)
Net Path Loss (dB) = FSPL (dB) − Gtx (dBi) − Grx (dBi)
FAQ
What is Free Space Path Loss (FSPL)?
Free Space Path Loss (FSPL) is the theoretical attenuation of electromagnetic radio frequency (RF) signal strength resulting from the natural geometric spreading of wavefront energy through an unobstructed vacuum or atmosphere according to the inverse-square law.
What is the Friis transmission equation?
The Friis transmission equation calculates received RF power based on transmitted power, distance, antenna gains, and wavelength: FSPL (dB) = 20 log₁₀(d) + 20 log₁₀(f) + 20 log₁₀(4π/c) − Gtx − Grx.
Why do higher frequencies experience greater path loss?
At higher frequencies (shorter wavelengths), the effective aperture area of an isotropic receiver antenna becomes smaller, capturing a smaller fraction of the expanding spherical electromagnetic wavefront.
Does FSPL account for trees, rain, or walls?
No. FSPL models ideal line-of-sight propagation through free space. In real-world environments, additional attenuation margins (Fresnel zone clearance, atmospheric absorption, vegetation, and building penetration loss) must be added to link budgets.
How we compare
| Feature | Online Tool Store | Telecom vendor spreadsheets | Manual logarithm formulas |
|---|---|---|---|
| Multi-unit distance & frequency conversions | ✓ | Partial | ✗ |
| Automatic RF wavelength calculation | ✓ | ✗ | ✗ |
| Antenna gain link budget integration | ✓ | ✓ | ✓ |