Friis Transmission equation (with dB units)


The Friis transmission equation is used in telecommunications engineering, and gives the power received by one antenna under idealized conditions given another antenna some distance away transmitting a known amount of power. The formula was derived in 1945 by Danish-American radio engineer Harald T. Friis at Bell Labs.

If the gain has units of dB, the equation is as shown here.

Related formulas


Prpower available at the input of the receiving antenna(in dBm) (dimensionless)
Ptoutput power to the transmitting antenna(in dBm) (dimensionless)
Gtantenna gain (with respect to an isotropic radiator) of the transmitting antennas (decibel)
Grantenna gain (with respect to an isotropic radiator) of (decibel)
λwavelength (m)
Rdistance between the antennas (m)