Ohms law, voltage and watts:

ohms is the electrical resistance to electricity of your coil

Volts divided by ohms = amps so @ 3.3 volts a 1.8 ohm coil will draw 1.83 amps

Amps x volts = wattage (power) so on an 1.8 ohm coil on the 3.3 volt setting will give your coil a 6.05 watt burn

3.3 volts on a 2.2 ohm coil = 1.5 amps x 3.3 volt would equal a 4.8 watt burn

and so on...

edit: as your battery voltage drops so will your output wattage across the coil and performance will dwindle