Basic Electromagnetic Fields (EMF) Calculator:

Transmitter Power:Watts (Power at the Transmitter)
Antenna Gain:dBi (Isotropic Radiator) dBd (½ λ Dipole)
Operating Frequency:MHz
Operating Mode:SSB/CW (50% duty) AM/FM/Data (100% duty)

This Electromagnetic Fields (EMF) Calculator makes the following assumptions;
1. All transmissions are at most 50% on and 50% off, such as having a QSO.

2. In addition to the 50% on, 50% off nature of all amateur transmissions, the calculator also accounts for Duty Cycle. SSB and CW are assumed to be 50% duty cycle, while AM/FM and Data modes are assumed to be 100% duty.

3. Transmitter power, is just that, the power output from your transmitter, this assumes 0dB coax loss, presenting a worst case scenario.

4. ERP is calculated based on 100% of the transmitted power reaching the antenna, and the antenna Gain you specify in dB, this dB value is expected to be dBd (gain relitive to a dipole antenna).

5. EIRP is calculated as ERP x 1.64 per the Ofcom calculator Linked Here

6. EIRP Average is calculated as EIRP x Duty Cycle x Transmitter On Time (assumed to be 50%, see above).

7. Exactly like the Ofcom calulator, this tool provides conservative seperation distance assuming that:
    i. Antenna height and pattern are not accounted for;
    ii. Typical ground reflection conditions (of 0.6);
    iii. Typical free space impedance (of 377 ohms);