The size of the trampoline you buy will depend on the amount of space you have for the trampoline and the age of the people who will be using it. For the first point, measure how much space you can allot to the trampoline. Pay attention to whether you can accommodate a round or rectangular trampoline. As for the second, the ideal-sized trampoline is directly related to the age of the bouncer. Toddlers up to three years of age will do best with a mini trampoline. Four to seven-year-olds will match with six-foot to 12-foot models, while older kids will need nine or 12-foot to 14-foot models. If you have large families, 14 feet or more will be satisfactory.