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Free Space Path Loss Calculator

Calculate free space path loss (FSPL) using frequency and distance. The Free Space Path Loss Calculator helps estimate how much signal power is lost when a radio wave travels through free space between a transmitter and receiver. Used in RF engineering, wireless network design, satellite communication, radar systems, and microwave links.

Calculate FSPL

Result

Enter frequency and distance to calculate.

FSPL -
Frequency -
Distance -

FSPL Formula

FSPL(dB) = 32.44 + 20 * log10(f_MHz) + 20 * log10(d_km)

Where f_MHz is frequency in MHz and d_km is distance in kilometers.

Free Space Path Loss (FSPL)

Free Space Path Loss (FSPL) depends mainly on two factors:

  • Distance between transmitter and receiver
  • Signal frequency

Higher frequencies and longer distances lead to greater signal loss.

Free Space Path Loss Formula

The most commonly used FSPL equation is:

FSPL(dB) = 20log10(d) + 20log10(f) + 32.44

Where:

  • d = distance between antennas (km)
  • f = frequency (MHz)
  • FSPL = path loss in decibels (dB)

The constant 32.44 accounts for the speed of light and unit conversions.

Alternative FSPL Formula (Meters and Hz)

If distance is in meters and frequency is in Hz:

FSPL(dB) = 20log10(d) + 20log10(f) - 147.55

Where:

  • d = distance (meters)
  • f = frequency (Hz)

Example FSPL Calculation

Suppose a wireless link operates at:

  • Frequency: 2.4 GHz
  • Distance: 1 km

Step 1: Convert frequency to MHz

2.4 GHz = 2400 MHz

Step 2: Apply the FSPL formula

FSPL = 20log10(1) + 20log10(2400) + 32.44

FSPL ≈ 100.04 dB

This means the signal loses about 100 dB of power over a 1 km distance in free space.

FSPL for Common Wireless Frequencies

Frequency Distance Path Loss
900 MHz1 km~91.5 dB
2.4 GHz1 km~100 dB
5 GHz1 km~106.4 dB
28 GHz1 km~121.4 dB

Higher frequencies experience greater free space loss.

Why Free Space Path Loss Matters

FSPL is critical in designing wireless systems because it helps engineers determine:

  • Required transmit power
  • Antenna gain
  • Expected coverage range
  • Link reliability

This calculation is the first step in creating a radio link budget.

FSPL in Real Wireless Systems

Cellular Networks (4G / 5G)

Used to estimate coverage of:

  • macro base stations
  • small cells
  • mmWave deployments

Higher frequencies such as 5G mmWave (28 GHz) suffer significantly higher path loss.

WiFi Networks

Used for planning:

  • outdoor WiFi links
  • point-to-point bridges
  • campus wireless coverage

Typical WiFi frequencies:

  • 2.4 GHz
  • 5 GHz
  • 6 GHz (WiFi 6E)