Free-Space Path Loss & Link Budget Calculator
FSPL from distance and frequency, plus a full link budget — TX power, antenna gains, RX sensitivity and fade margin verdict.
Free space is the BEST case — real links lose more to ground reflections, foliage (~0.3 dB/m), walls (3–10 dB each) and rain above 10 GHz. Plan ≥ 20 dB fade margin for anything outdoors. Doubling distance always costs exactly 6 dB; doubling frequency also costs 6 dB, which is why sub-GHz IoT links go so much farther than 2.4 GHz at the same power.
Disclaimer: This tool is for general informational and estimation purposes only and is not professional financial, tax, accounting or legal advice. All figures are estimates — verify with a qualified professional before making decisions. Read the full disclaimer.
Free Space Path Loss Calculator computes path loss over distance and frequency, plus a complete link budget with margin — free, instant and private in your browser. LoRa/IoT deployers, WISP planners and ham operators budgeting a link use it to skip the datasheet algebra: type your numbers, read the answer with the substituted formula shown step by step, and share an exact permalink of the calculation.
About Free-Space Path Loss & Link Budget Calculator
Free Space Path Loss Calculator computes path loss over distance and frequency, plus a complete link budget with margin using the standard engineering relation: FSPL(dB) = 20log₁₀(d_km) + 20log₁₀(f_MHz) + 32.44; P(rx) = P(tx) + gains − FSPL. Worked live: 5 km at 868 MHz loses 105 dB — a 14 dBm LoRa node with 2 dBi antennas still lands ~33 dB above a −120 dBm receiver. The result recalculates on every keystroke, the worked-example panel shows your numbers substituted into the formula, and the Copy permalink button encodes the inputs in the URL so a colleague opens exactly your calculation. Everything runs client-side — nothing you type leaves your device.
How to use Free-Space Path Loss & Link Budget Calculator
- 1Enter your values — the tool starts with realistic defaults for this exact use case, so the worked example is meaningful immediately.
- 2Read the live result and the worked-example panel, which substitutes your numbers into the formula step by step.
- 3Adjust any input to compare scenarios, then use Copy result or Copy permalink to share the calculation.
Why use Free-Space Path Loss & Link Budget Calculator?
- ✓Implements the real formula — FSPL(dB) = 20log₁₀(d_km) + 20log₁₀(f_MHz) + 32.44 — with the substitution shown, not a black box
- ✓Built for LoRa/IoT deployers, WISP planners and ham operators budgeting a link
- ✓Copy result and permalink buttons — share the exact calculation in a README, forum answer or design review
- ✓100% free, no sign-up, runs entirely in your browser (works offline once loaded)
Frequently asked questions
How do you calculate free space path loss?+
Path loss over distance and frequency, plus a complete link budget with margin follows FSPL(dB) = 20log₁₀(d_km) + 20log₁₀(f_MHz) + 32.44; P(rx) = P(tx) + gains − FSPL. For example, 5 km at 868 MHz loses 105 dB — a 14 dBm LoRa node with 2 dBi antennas still lands ~33 dB above a −120 dBm receiver. The calculator applies the same relation and shows the substituted arithmetic so you can verify every step.
How much link margin should I design for?+
≥ 20 dB for outdoor links: rain, foliage growth, multipath fading and antenna aging all take bites. 10 dB works for short clear shots; below that expect seasonal dropouts. Indoor adds 3–10 dB per wall on top of FSPL.
Why do sub-GHz links go so much farther than 2.4 GHz?+
FSPL grows 6 dB per frequency doubling — 868 MHz enjoys ~9 dB less path loss than 2.4 GHz over the same distance, plus better diffraction around obstacles. That's LoRa's whole game; the price is far less bandwidth.
Is the Free Space Path Loss Calculator free and private?+
Yes — completely free with no sign-up or usage limits, and it runs entirely in your browser: the values you enter are never uploaded or stored on a server.
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