How Much Ham Do I Buy If It Is Bone In?

We are hosting a lunching for the 90th anniversary of our church. It is a pot luck but we will be provided the brisket and ham. We are buying precooked spiral sliced ham from Sam’s and since it is buffet and people will be serving themselves we are allowing 5 ounces per person.
HOWEVER, spiral sliced ham have the bone in them so buying per ounce is tricky? Does anyone have any idea how much to allow for the bone?