Friis Free-Space Path Loss (FSPL dB) & Wireless Link Budget Calculator

Compute wireless FSPL (dB) and received signal level for Wi-Fi, LoRa, or microwave links.

Free-Space Path Loss (FSPL)
121.69 dB
Expected Received Power (RSSI) -77.69 dBm
Link Margin Above −80 dBm Floor 2.31 dB
Carrier Wavelength 5.17 cm
Inputs
km
Line-of-sight link distance in kilometers.
MHz
Carrier frequency in Megahertz (e.g., 915, 2400, 5800 MHz).
dBm
Transmitter output power in dBm.
dBi
Combined Tx + Rx antenna gain minus cable loss in dBi.
Results & Graph
Free-Space Path Loss (FSPL)
121.69 dB
Expected Received Power (RSSI)
-77.69 dBm
Link Margin Above −80 dBm Floor
2.31 dB
Carrier Wavelength
5.17 cm

Free-Space Path Loss (FSPL)

Graph 1 • Distance Km Sensitivity Recalculates the domain equation across 50% to 150% of the primary input while holding other parameters constant.
0 dB 67.6 dB 135.2 dB 50%: 115.67 dB 115.7 50% 75%: 119.19 dB 119.2 75% 100%: 121.69 dB 121.7 100% 125%: 123.63 dB 123.6 125% 150%: 125.21 dB 125.2 150%
Graph 2 • Primary & Supporting Metric Comparison Compares the primary output alongside supporting domain benchmarks.
Free-Space Path Loss (FSPL) 121.69 dB Expected Received Power (RSSI) -77.69 dBm Link Margin Above −80 dBm Floor 2.31 dB Carrier Wavelength 5.17 cm
Graph 3 • Exact Output Table & Units Displays each calculated output in its exact domain unit.
Free-Space Path Loss (FSPL)121.69 dBExpected Received Power (RSSI)-77.69 dBmLink Margin Above −80 dBm Floor2.31 dBCarrier Wavelength5.17 cm
Summary: Across 5 km at 5800 MHz, Free-Space Path Loss is 121.69 dB and expected received signal strength (RSSI) is -77.69 dBm.
Summary: Across 5 km at 5800 MHz, Free-Space Path Loss is 121.69 dB and expected received signal strength (RSSI) is -77.69 dBm.
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Formula & Mathematical Methodology: Free-Space Path Loss Systems Engineering Formula

FSPLdB = 20·log₁₀(Distancekm) + 20·log₁₀(FreqMHz) + 32.44
RxdBm = TxdBm + Gtx + Grx − FSPLdB
FSPL_dB = 20·log₁₀(Distance_km) + 20·log₁₀(Freq_MHz) + 32.44; Rx_dBm = Tx_dBm + G_tx + G_rx − FSPL_dB
  • distanceKm: Distance Km (km)
  • frequencyMhz: Frequency Mhz (MHz)
  • txPowerDbm: Tx Power Dbm (dBm)
  • combinedAntennaGainDbi: Combined Antenna Gain Dbi (dBi)

Rounding: Binary/decimal capacities and engineering metrics retain full floating-point precision and round to 2 decimal places.

Worked Example: Architecture Sizing Example: Free-Space Path Loss

Compute wireless FSPL (dB) and received signal level for Wi-Fi, LoRa, or microwave links.

  1. Enter the workload parameters, model dimensions, or network link specifications.
  2. Compute the sizing equation: FSPL_dB = 20·log₁₀(Distance_km) + 20·log₁₀(Freq_MHz) + 32.44; Rx_dBm = Tx_dBm + G_tx + G_rx − FSPL_dB.
  3. Inspect the primary capacity metric, headroom buffers, and 3 SVG visualizations.
Result: Calculates Free-Space Path Loss via FSPL_dB = 20·log₁₀(Distance_km) + 20·log₁₀(Freq_MHz) + 32.44; Rx_dBm = Tx_dBm + G_tx + G_rx − FSPL_dB.

Frequently Asked Questions

How does the Friis Free-Space Path Loss (FSPL dB) & Wireless Link Budget Calculator compute capacity?

It evaluates FSPL_dB = 20·log₁₀(Distance_km) + 20·log₁₀(Freq_MHz) + 32.44; Rx_dBm = Tx_dBm + G_tx + G_rx − FSPL_dB directly in your browser and plots three custom SVG diagrams.

Can I compare different cluster or model configurations side by side?

Yes. Use the "Compare (0/3)" button in the results panel to pin up to three configurations.

Does this tool upload any of my architecture parameters?

No. All calculations run 100% client-side in your browser.

Science & Engineering · Electrical & RF Engineering

Friis Free-Space Path Loss (FSPL dB) & Wireless Link Budget Calculator: inputs, method, and how to read the result

Compute wireless FSPL (dB) and received signal level for Wi-Fi, LoRa, or microwave links.

Choose inputs for the case you are checking

The defaults are illustrative. Replace them with values for your case and keep the units shown beside each field.

  • Distance Km: Line-of-sight link distance in kilometers.
  • Frequency Mhz: Carrier frequency in Megahertz (e.g., 915, 2400, 5800 MHz).
  • Tx Power Dbm: Transmitter output power in dBm.
  • Combined Antenna Gain Dbi: Combined Tx + Rx antenna gain minus cable loss in dBi.

What the calculation includes

With the default values shown, Free-Space Path Loss (FSPL) is 121.69 dB. The calculation follows Free-Space Path Loss Systems Engineering Formula; the formula and variable definitions above show how the inputs combine.

One-input check: With the other defaults held constant, changing Distance Km from 5 km to 6 km changes Free-Space Path Loss (FSPL) from 121.69 dB to 123.27 dB. This is a comparison inside the calculator's stated model, not a prediction.

Where to use caution

  • Uses industry-standard IEEE, IETF RFC, and GPU/cloud hardware sizing conventions.
  • Capacity planning estimate; benchmark under production traffic patterns before finalizing cluster or hardware procurement.

Scope: IEEE / IETF / Cloud Systems Engineering Standard Check the assumptions and limitations against your situation before relying on the estimate.

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