6-to-8 weeks, if you file by mail and wait for the check to arrive in the mail. 6 weeks in January, 8 weeks after that.
3-to-4 weeks if you electronically file and wait for the check in the mail. 3 in January, 4 after that.
2-to-3 weeks if you file electronically and direct the IRS to electronically transfer your refund into your checking or savings account. The refund is issued 2 Fridays after you file, your bank takes several days to actually credit your account.
If you file through a tax prep service that offers refund anticipation loans, for a fee you can get your refund (a bank loan on your refund that will pay off the loan in two Fridays) in 48 hours or less.