Ring game - level terminology

When people talk about playing a $50NL or $100NL ring game, I understand that this is the buy-in amount... but....

Is it the minimum or maximum buy-in?
What blinds/bets = these levels?

The sites I play on list the blind levels (or is it the bet levels?) but they don't say $50NL buy-in next to it.

Is there a table that will say something like;

Blinds(or bets?) buy-in
0.05/0.10 10
0.10/0.20 20

... or a formula (ie, small bet x 20 = level?)

Thanks

(PS, I'm having a bad couple of days with my SNG playing, the £3.00 jump didn't work as well as I had hoped, I'm down to about £70 BR now...)

Its the maximum buy-in.

025/050 = 50$
050/1 = 100$

structure is simple

yep, usually 100 x the big blind