Jesskerch:
I am not a lawyer, but from my experience, it all depends. It is better to agree upon an amount with your ex beforehand, becasue if you don't then the judge will decide, and that judgement may not be as good for you as your pre-arranged agreement. The lawyers can write it up and give it to the judge.
Some of the things it depends on are if either of you work or not, if either of you EVER worked or not, how many years you were married, how valuable to society the wife would be without support (education, previous jobs).
The length of the marriage has a lot to do with it, but there's no single calculation such as percentage of income that determines alimony in Ohio, that I know of.