I'm assuming you're not a DOT regulated transportation worker.

For travel on business, overnight, away from home the per diem rate varies from location to location. From IRS Publication 17: "Amount of standard meal allowance. The standard meal allowance is the federal M&IE rate. For 2015 the rate in most small localities is $51 a day." For more specific rates, see http://www.gsa.gov/perdiem as the actual rate depends on the location of your travel. (Note that you need to set the year in the drop down box just above the map.)