What Size bike?
I want to buy a on the internet. Ijust don't know which size would be right for me, e.g. 16" 17" 18"
I'm about 5" 5
we be rollin'
I like the coloradocyclist link above. It depends on whether you want a mountain or road. You can check out the thread I started in the Touring forum. I got some answers there on my own sizing. My wild guess is you may need something like 16 inch. I'm 5'8" and usually wear 31 length pants and in department store bicycles, I usually take an 18 inch. Of course, the 54cm model I chose for my touring frame is seems a little tall for me so I may want 52cm for off-road.
DRF aka Thrifty Bill
+1 Not enough information. What type of bike?
+1 That Colorado cyclist is a good place to start.
Oversimplification, but women at a given height tend to have longer legs than males. I have had a woman 5-7 fit a larger bike than I fit at 5-11. Lots of variables. If you are buying new, nothing beats a really good bicycle shop at getting it right.
On vintage road bikes, I start with this chart to get in the ballpark: