Use the battery drain section.
Fill out the ohms of resistance your gonna use then select the batteies....Or plug in the presets for prospective acquisitions...
Keep at least 30% headroom unless your one of those "ragged edge" folks.
Anything under 10% headroom is trouble since coils may change 10% due to temperature variances and connection loss will also increase/decrease on newbie coils/builds.....(not trying to jab ya....If ya van build the same coil 3 times and get it to measure ON THE MOD what is measures on the meter your no longer a newbie!)
IMHO YMMV!
I vape a Kayfun on efest 20amp batteries and jeep my builds above .8 ohms. According to the calc I can go to .4 but I dont trust the batteries to perform that well and I dont like charging batteries all day.
That and the kayfun doesn't really have the airflow for .4