According to Playintennis5274 :
electric is way better than gas IF you have the choice. less noise and electric
is like 60% more efficient. But if yourr in construction, gas might be better
but i guess you can tap off the temp pole. Anyways. the biggest thing you need
to know in "how big" is figure what tool uses the most "csfm" toolowners manuel
will list in the specs. "CSFM" is cubic square feet per minute. Most tools
will use aroun 4-7.5 . see how much each nail gun uses , add that and get a
compressor that is listed to put out that many csfm.

Cubic square feet?

Ahem.

You mean CFM. There's no square feet in cubic feet ;-)

Nail guns don't use very much CFM. Usually less than 2, depending on how fast
you go and what size nails you're firing.

My home brew air compressor with a 10 gal tank goes about half-hour between
recharges with a 18ga nailer... Which is good, because the compressor is about
3/4 CFM.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.