Once a week, measure the output twice, once at 'full' and then later at 'stretched' and record bladder volume. Use a big glass measuring cup from the kitchen. Just handle it carefully and wash it well when you are done. Typically, kids age five through puberty notice that they have a full bladder when it holds about the same as their age in ounces. Most can delay voiding long enough to hold one to two ounces more than their age.
Some people feel full at as little as half the desired volume.
An increase in the difference between 'full' and 'stretched' can help reduce daytime urgency wetting, but increasing the volume at 'full' may make more difference in how soon a sleeping person's bladder empties itself. The first objective is not to delay sleepwetting all the way until morning, but just past the first two and a half or three hours of deepest sleep. Always consult a doctor for medical diagnoses and treatments. I have researched the area of teaching bladder control and managing bladder disabilities as part of volunteer work with incontinence support organizations and families of children with disabilities. I am a writer, actor, storyteller, children's bookseller, and parent of two young adults.