A Christmas tree should be tall enough to reach the ceiling and fill the room with a festive atmosphere, but not so tall that it becomes a safety hazard or blocks the view of your holiday decorations. Generally, a good rule of thumb is to choose a tree that is about six to eight feet tall, depending on the size of your room and how many decorations you plan to hang. If you have a small space, you can also consider a tabletop tree, which is typically about three to four feet tall.