In radio systems the EIRP (equivalent isotropic radiated power) is the amount of power that an isotropic antenna would emit to produce the peak power density observed in the direction of maximum antenna gain. The EIRP and power are stated in dBm (decibels in milliwatts), also known as dBmW, or dBW (decibels in watts); cable loss is stated in dB (decibels); and the antenna gain is stated in dBi (decibels referenced to an isotropic antenna).

Determine the values you will be using for your transmitter output, antenna gain and line loss.

Enter your values into the following formula. EIRP = Pout (TX output power) + G (antenna gain)  L ( line loss).

Perform the calculations. Example:
Transmitter power = 25 dBm
Antenna gain = 15 dBi
Line loss = 9.6 dBEIRP (dBm or dBW) = P (dBm or dBW) + G (dBi)  L (dB)
EIRP = 25 + 15  9.6
EIRP = 30.4 dB
Tips & Warnings
 Every 10 dBm adds a zero to the mW value.
 0dBm = 1 mW
 10dBm = 10 mW
 20dBm = 100 mW
 30dBm = 1,000 mW or 1 Watt
 40dBm = 10,000 mW or 10 Watts
 This article is intended for those with WAN or radio signal experience.