This seemed like the best place to ask

im confused on how big of a generator i need

I use a small fan
also a 75amp 12v power supply for my duo Hyperion 720 charger

charging 14.8 lipo 3600 at about 6 amps
7.4v lipo 5200 at 8 amps
7.2v life 3200 at 5 amps

usually charging two of the three at same time with fan running

1000watts should run everything you have and then some

is there a way to calculate how many watts im using?

There is. However I do not know it. Your power supply is a 75 amp you said. But remember your only pulling 10 amps or so per channel of your charger. So at most I'd say your pulling 25 amps on the charger, plus a fan or whatever else you use.

You could google how to calculate your amps into watts.

Watts = Amps x Volts

Your power supply is 75a x 12v so it's 900 watts, but you won't necessarily be using all 900.

14.8v x 6a = 88.8w
7.4v x 8a = 59.2w
7.2v x 5a = 36w

Conservatively, you'll likely use less than 250w for your charger. A box fan shouldn't pull more than 100w or so. A 1kw (1,000 watt) generator should more than do it.

Assuming that your power supply is 80% efficient:
((14.8 * 6) + (7.4 * 8) + (7.2 * 5)) / 0.8 = 230 watts.

The fan probably says how much it uses on a label.