Min. amount of taxable income for a full refund of fed. taxes, single?

I promises to help my boyfriend do his taxes on turbo tax right after I did mine for myself and my company. I have finished mine so now I have to do his. I know after speaking with my mother that there is a way that he can ge a full refund for all the federal income taxes he paid if he makes under a certain amount or has a taxable income, after deductions lower then a certain amount. Can anyone tell me what that amount is? he filed as single. Thank you in advance!