On the left hand side of your federal tax return, you should see a box that says "Standard Deduction for-". Check that box for the standard deduction that corresponds to your filing status for that year. If the amount in box 12 corresponds to your standard deduction, your state tax refund is not taxable.
If you don't remember what your filing status was, look at the very top of the return above your name and social security number. There will be a box checked that tells you your filing status.
