There's not really any official percentage. It depends how much you made, how much you owe, and how much you've already paid (withheld from paycheck and/or made estimated payments.) Assuming you can't be claimed on your parents' taxes, your standard deduction is $5700, and personal exemption is $3,650. Those would get deducted from the tax you owe the government, and anything you paid over and above what you owe, you'll get back. Depending on how much you make, you also could get an Earned Income Credit, and/or a Making Work Pay credit of $400.00.
Let me add this, though. Getting money back means the government had your money through the end of the year, and didn't pay you any interest. That's not such a good thing. On the other hand, if you know you'd spend it all from your paycheck immediately, you may be better off this way. It's like a form of forced savings, if you invest your refund.