RF calculator
Free-space path loss calculator
Calculate free-space path loss from distance and frequency using the ITU‑R P.525 formula.
Need this in code or an AI agent? Call it as a free API.
What free-space path loss means
Free-space path loss describes geometric spreading for an unobstructed far-field path. It increases by about 6.02 dB whenever distance doubles and by the same amount whenever frequency doubles.
Worked example
At 5.5 GHz over 10 metres, the basic transmission loss is approximately 67.26 dB. A 20 dBm transmitter with 4 dBi gain would have roughly −43.26 dBm available before receiver gain and other losses.
Indoor walls and site-specific effects are not part of FSPL. Read Indoor RF path loss and wall attenuation before applying it to a building.
Source
ITU‑R Recommendation P.525, Calculation of free-space attenuation.
What this doesn't model
- Walls, floors, glass, and furniture. The number is for a clear path only.
- Where the access point should go. Distance alone does not place a radio.
A SiteRF project puts the floor plan, the materials in its walls, and the radios in one model, and shows predicted signal strength across the plan.
Related free tools
Free API
Free-space path loss as an API
The same calculation over HTTP. Send the parameters in the query string or as JSON and get the result back with its formula and assumptions.
No API key. GET or POST. Every result carries its formula, assumptions, and source.
Request
curl -G "https://siterfapp.com/api/v1/tools/free-space-path-loss" \
-d distance=10 \
-d distance_unit=m \
-d frequency=5.5 \
-d frequency_unit=GHzResponse (abridged)
{
"tool": "free-space-path-loss",
"inputs": {
"distance": 10,
"distance_unit": "m",
"frequency": 5.5,
"frequency_unit": "GHz"
},
"result": {
"path_loss_db": 67.25503701176825,
"distance_m": 10,
"frequency_hz": 5500000000
},
"next_steps": [
{
"id": "rf_solve_coverage",
"why": "This is free-space path loss: walls, floors and furniture are not modelled. Coverage across a whole building needs a floor plan.",
"requires": "account_with_approval",
"status": "available",
"learn_more": "https://siterfapp.com/agents/#rf_solve_coverage"
}
]
}