The average size for a sauna is about 4 feet by 6 feet or 5 feet by 7 feet. This is enough for 2 to 3 people. You will find that some saunas will be about twelve feet by twelve if the sauna needs to be used by a lot of people at the same time. This is the more common size for public saunas. Small at home saunas are usually in the 4'6 size range but this might be too small if you are going to be using your sauna with guests and other people. For most people who are using their sauna daily, the smaller sauna is easier to maintain and set up, and that makes it attractive.