Free Space Path Loss Calculator
Enter frequency and distance to instantly compute free-space path loss (FSPL) in dB using the Friis transmission equation.
Signal Parameters
Quick Presets
Friis Formula
FSPL(dB) = 20·log10(d)
+ 20·log10(f)
+ 20·log10(4π/c)
+ 20·log10(f)
+ 20·log10(4π/c)
d in meters, f in Hz, c = 3×108 m/s
Simplified (km, MHz): FSPL = 20·log10(d) + 20·log10(f) + 32.45
Formula Breakdown
FSPL vs Distance
at current frequencyEnter frequency and distance, then click Calculate Path Loss.
Summary
Enter frequency and distance to instantly compute free-space path loss (FSPL) in dB using the Friis transmission equation.
How it works
- Enter the signal frequency and select the unit (MHz or GHz).
- Enter the path distance and select the unit (m, km, or miles).
- Click Calculate to compute FSPL in dB using the Friis equation.
- Review the result along with a breakdown of each term in the formula.
- Adjust frequency or distance to see how each affects path loss.
Use cases
- Estimating signal attenuation for Wi-Fi, LTE, or 5G outdoor links.
- Satellite link analysis — computing path loss over thousands of kilometers.
- LoRa and IoT network coverage planning for outdoor deployments.
- Amateur radio (ham) contact planning on VHF, UHF, and microwave bands.
- Classroom and lab exercises on RF propagation fundamentals.
- Quick sanity checks on antenna gain and transmit power requirements.
- Drone and UAV communication range estimation.
- Radar system design — calculating round-trip free-space loss.
Frequently Asked Questions
Last updated: 2026-07-01 ·
Reviewed by Nham Vu