Free-Space Path Loss & Friis Received Power
Free-space path loss from frequency and distance, plus received power via the Friis equation.
Worked example
Input: Frequency 1000 MHz, Distance 3 m, Transmit power 0 dBm, Tx antenna gain 0 dBi, Rx antenna gain 0 dBi
Result: Path loss 41.9902 dB, Received power -41.9902 dBm
Result: Path loss 41.9902 dB, Received power -41.9902 dBm
Formula
FSPL = 20·log₁₀(4π·d·f / c)
P_r = P_t + G_t + G_r − FSPL
How it works
Free-space path loss is FSPL = 20·log₁₀(4πdf/c). Add transmit power and both antenna gains, subtract the path loss, and you get received power. Useful for wireless-module interference checks, link budgets inside a chamber and for understanding site attenuation.
Practical tipFriis is only accurate in the far field. In a 3 m chamber, frequencies of a few tens of MHz and below are not in the far field and floor reflections matter, so treat the result as a rough estimate.
Related calculators
Results and summaries are for reference. For certification and test reports use the latest official standard text and calibrated instrument data. Last updated: 2026-10-10