Convert antenna gain between dBi and dBd, and work out ERP and EIRP from transmit power, feedline loss and antenna gain.
Gain in dBi is referenced to an isotropic source, dBd to a dipole; dBi = dBd + 2.15. EIRP uses the dBi gain, ERP uses the dBd gain: effective power = TX power minus feedline loss plus antenna gain, in dB. This is how regulators express the radiated power limit.
dBi is gain compared to a theoretical isotropic radiator, dBd is gain compared to a half-wave dipole. A dipole has 2.15 dBi of gain, so dBi = dBd + 2.15. Manufacturers often quote dBi because the number looks larger.
Both are the effective radiated power after feedline loss and antenna gain. ERP is referenced to a dipole (uses dBd gain), EIRP to an isotropic source (uses dBi gain), so EIRP is always 2.15 dB higher than ERP for the same antenna.
Work in decibels: take the transmit power in dBW, subtract the feedline loss in dB, and add the antenna gain in dBd. Convert back to watts. So 100W with 3 dB of feedline loss and a 6 dBd antenna gives about 200W ERP.