Free · Physics models
Free-Space Radio Link Loss with Antenna Gains
Estimate ideal radio link attenuation from free-space spreading, after subtracting transmitter and receiver antenna gains in dBi.
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Calculator inputs
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How to use this calculator
- Enter the known values in the units shown. Results update as you type.
- Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
- Use the worked example to check the method. Reset restores the starting fields.
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Formula and method
fspl = 87.441772.
L = 20 log₁₀(4πdf/c) − Gt − Gr, with c approximated as 3 × 10⁸ m/s.
Worked example
Enter these known values and leave the other values blank.
- Distance (d)
- 1 km
- Frequency (f)
- 1 GHz
- Transmitter gain (Gᴛ)
- 2 dB
- Receiver gain (Gʀ)
- 3 dB
- Free space path loss (FSPL)
- 87.44 dB
Assumptions and limitations
- Estimate ideal radio link attenuation from free-space spreading, after subtracting transmitter and receiver antenna gains in dBi.
- This model uses the rounded propagation speed 300,000,000 m/s. Antenna gains are already subtracted from the result; do not subtract them again in a link budget.
- Assume unobstructed far-field propagation, matched polarization and positive distance and frequency. Terrain, rain, absorption, cables and mismatch losses are excluded.
- Inputs and inverse outputs share the displayed unit selectors. Clear a known field to solve for it, and lock quantities that must remain fixed. Singular inverses may have no finite result.
Common questions
Is the result bare path loss?
Only with both antenna gains set to zero. Otherwise it is the free-space attenuation after both gains.
Can it model an indoor link?
It omits walls and reflections; use it as an ideal spreading reference.
References
Estimate ideal radio link attenuation from free-space spreading, after subtracting transmitter and receiver antenna gains in dBi. This model uses the rounded propagation speed 300,000,000 m/s. Antenna gains are already subtracted from the result; do not subtract them again in a link budget. Assume unobstructed far-field propagation, matched polarization and positive distance and frequency. Terrain, rain, absorption, cables and mismatch losses are excluded.