This calculator converts volt-per-meter (V/m) to dBm.
V/m is a measure of field intensity at any distance from the transmitter. The signal at the input of the receiver however is typically specified in terms of Volt or dBm.
There are two calculators to convert from V/m to dBm.
The first one requires the Antenna gain and Frequency of operation. It uses this to compute the Antenna Factor and then dBm.
This next calculator is used if you know the antenna factor. Many antenna vendors will provide this in a data sheet as a function of frequency. Use this number directly.