I have always went by what my mother taught me (mother knows best). Hams are best when cooked at 325 degrees F with a little water in the bottom of the roasting pan. I say a little because ham will render juices out as it cooks. Just enough to cover the bottom of the pan. Figure at least 15 to 18 minutes per pound. The ham is already cooked so you are just warming it through really. And don't forget a lid or foil to cover it, which will keep it from drying on the outside while the inside heats through. Hope it helps.