The short answer is that a nonprovisional utility patent usually lasts for twenty years from the date of first filing. The slightly longer answer, per the USPTO website is, "The term of a utility or plant patent generally lasts 20 years from the date the application was filed in the United States or, if the application specifically refers to an earlier application filed under 35 U.S.C. 120, 121 or 365(c), from the earliest date of filing and subject to payment of maintenance fees." It's important to be clear though that patent rights are limited to the 'right to exclude', which you can also read more about on the linked USPTO page above.
If you would like to be guided to further resources on this subject, please email the PTRC Representatives at lib-ptrc@osu.edu.
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