I just realized I have been using the fighter/bomber space as a figure for their size. I've been thinking, "parasite carrier has 110 space, fighters are 11 space(size), ten will fit."
For carriers and ships designed to hold Small craft, this is actually exactly how you would count it. They're specifically designed for maximum storage and flexibility.
As far as yachts and Corvettes, I checked my numbers. You actually can hold two Yachts in the fighter bay of a Parasite Carrier with, oh, about two 45' shipping containers worth of extra space (which will, inevitably, be used for alcoholic purposes.) On the other hand, you could hold one Corvette in the same space, barely. You conceivably *could* fit in a second one in, if you don't actually carry anything else whatsoever and trust your engineers to not remove something important and not mess with the profile too bad when extending the cargo hold, but at that point you're going to take mass penalties and lose about 40g of acceleration.
That might help give you a bit of scale, actually. In terms of "space", a Corvette has a score over 120. That's significantly bigger than a Fighter.
I have personally imagined a fighter as something about 70 feet long, 12 foot high, 14 foot wide or so, with just about the size of a 40 foot shipping container left over after weapons, drive, life support, power plant, etc, etc. I reckon that's about a 26.5 space.
By comparison, a Waller would be at least size 2450. A Megafreight is about 6000.
I'm sure someone who is better at science than I can come up with at least 2 reasons why I am wrong, but that doesn't particularly matter. *shrugs