Wi-Fi EIRP Calculator
As a Wi-Fi engineer, there are a number of occasions when it is useful to understand the EIRP ("Effective Isotropically Radiated Power) of a system. (I'll leave to you to read this Wikipedia link for an EIRP explanation). This is often a requirement when using external antennas on an access point or perhaps using tools (e.g. survey software) which require you to account for the various gains and losses in a system.