The Friis transmission equation, as shown below, gives the ratio of received to transmitted power for given antenna gains, ranges, and wavelengths under ideal conditions. The calculator below uses this equation to find any one of the variables, provided all the other variables are known.

Leave the unknown value blank and fill in the remaining values. When one available unit for a value is filled in, the other available units are automatically converted from the entered unit value. Once all but one value is entered in, press Calculate next to the unknown value.