How far into training are you? My last marathon cycle had a run about 2 months out that was 3 mile warm up + 10 at marathon pace + 3 mile cool down and I used a half to do the workout with a few miles before and after. If you are going to try to do an equivalent pace I use the VDOT calculator and would shoot for 7:43 pace.
I'm going to be contrarian and say you should run at your marathon pace. When you do race your full, the first 16 miles or so should feel very easy. What better way to test that than by running a half at your goal pace. It's a perfect opportunity to simulate your race nutrition and fueling too. If it does feel easy, you can bank that feeling and recall it on race day. If it doesn't feel easy, you'll know you're not there yet and need to boost your fitness and endurance over the next few months before the race.
