Do you know the bladder capacity of the average 9 yr old child?

11 oz, or 330 mL. Rule of thumb is a childs bladder capacity should be their age inyears +2 oz. Thus 11 oz for a nine year old.
Age + 2 (in ounces) The way to estimate a child's bladder capacity is to take the age of teh child (in years) and add 2. This give the number of ounces that a child's bladder can hold. So, a 9 y/o child will hold 9+2 = 11 ounces.