While 12-person tents are designed with larger groups in mind, the truth is most families decide to go for a big tent for a more comfortable sleeping experience. For this reason, you should actually consider the floor size and the number of people/quantity of gear you want to fit in the tent.
For instance, if you need a big tent for 6-8 people sleeping on cots or air mattresses, you could choose a tent with a more compact footprint. While you’ll still have plenty of space for your gear, a smaller 12-person tent packs more compactly and is easier to store and transport.
However, if you need a tent that can fit 12 adults, consider the average size of a person and account for at least six inches of space between the occupants.
Another important thing to check out is the standing height. Most 12 person tents have high ceilings that allow you to stand and move freely, but if you’re particularly tall, make sure the tent is big enough for you.