What is free-space path loss?

Free-space path loss (FSPL) is the reduction in signal power as an electromagnetic wave travels through free space (vacuum or open air with no obstructions). It results purely from the spreading of the wavefront over a larger area as distance increases — not from absorption or reflection.

What formula does this calculator use?

FSPL(dB) = 20·log10(d) + 20·log10(f) + 20·log10(4π/c), where d is distance in meters, f is frequency in Hz, and c is the speed of light (≈ 3×10⁸ m/s). This simplifies to FSPL(dB) = 20·log10(d_km) + 20·log10(f_MHz) + 32.45 when using km and MHz.

Does path loss increase with frequency?

Yes. Doubling the frequency adds approximately 6 dB of path loss. This is why higher-frequency bands (5 GHz Wi-Fi, mmWave 5G) have shorter range than lower-frequency bands (900 MHz LoRa, 700 MHz LTE) at the same transmit power.

Does path loss increase with distance?

Yes. Doubling the distance adds approximately 6 dB of path loss (inverse-square law). Every decade in distance (e.g., 1 km to 10 km) adds 20 dB.

Is FSPL the same as total link loss?

No. FSPL is just one component of the total link budget. Real links also include cable and connector losses, atmospheric absorption, rain fade, multipath fading, and diffraction losses. FSPL provides the baseline for any line-of-sight link analysis.

What units does this calculator output?

Path loss is expressed in decibels (dB), which is the standard unit in RF engineering. A higher dB value means more attenuation. Typical FSPL values range from ~40 dB (short-range indoor links) to over 200 dB (satellite links).

Free Space Path Loss Calculator

Name: Free Space Path Loss Calculator
Availability: InStock
Author: Nham Vu

Enter frequency and distance to instantly compute free-space path loss (FSPL) in dB using the Friis transmission equation.

Signal Parameters

Frequency

Distance

Quick Presets

Friis Formula

FSPL(dB) = 20·log₁₀(d)
+ 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

Enter 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

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Last updated: 2026-05-23 · Reviewed by Nham Vu