How many people should be on a trampoline?

On a 13 to 15' trampoline I would recommend 4-5 children at once. I have 4 kids around the same age and they have been following this rule for 5 years on my 14' trampoline and no one has gotten more than a scrape. Doing flips and bouncing high has also not caused any damage to my children s bodies. I believe that trampolines are a safe form of exercise.