A 13.5 pounder is the Goldilocks turkey. Not too big, not too small. It cooks evenly and feeds about 10 people (with leftovers for sandwiches).
At 325°F, you’re looking at a 3-hour to 3-hour-45-minute window, depending on your oven’s mood swings.
Use an instant-read thermometer every 30 minutes after the 2.5-hour mark. And don’t be shy—poke that thigh like you mean it.