If my status is single without dependents what's the average withholding percentage at a job?

Your withholding will be determined in part by what you put down on your W-4 that you give to your employer.

You can see what your withholding will be by using this calculator:

http://www.paycheckcity.com/NetPayCalc/netpaycalculator.asp

If you need help filling out your W-4, use this calculator:

http://www.paycheckcity.com/w4/w4instruction.asp