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How Big Is Your Child’s Bladder?

  • 3 minute read

How Big is Your Child’s Bladder?

Most likely not something you’ve thought about, but quite interesting, nonetheless.

Many parents don’t know how much the size of their child’s bladder can play into the toilet training process! Even if you’re armed with a mattress protector, if your child’s bladder isn’t big enough to hold the wee, then they probably can’t make it to the morning dry. That’s typically why most parents wait until their child is slightly older before beginning their night-time toilet training practices.

 Even if you’ve never thought about your child’s bladder size, it can be an interesting topic to investigate. Come along with me as I investigate how to calculate the size of a child’s bladder, and what ‘normal’ really means in the context of bedwetting.

A ‘Normal’ Bladder – What You Should Know 

We have previously talked about bedwetting being a normal part of growing up. As parents, we know that for the most part, ‘normal is as normal does’. However, this got me thinking about what a normal bladder does and doesn’t do! So, I decided to do some research into the typical size of bladders, and to see if there was a way to calculate it for children. After I set about discovering, here’s what I found out.

Interestingly, some of the easiest to understand information about how a normal bladder works came from the . While this is not necessarily a site you may have visited in pursuit of this question, it provides a great explanation about both volume and frequency. Basically, a normal adult bladder holds 300-500mls of fluid (that’s about half a pint to a pint), and we typically empty our bladders between 6 and 8 times a day.

Children are, of course, smaller. Not to mention, with all their activity they can sweat out quite a lot of fluid in a day! So, for them, the normal range for bladder emptying is between 4 and 8 times a day. That explains why the bedwetting alarm goes off so often at night!

It’s All Greek to Me: The Formula for Calculating Bladder Size 

One of the most interesting discoveries I found is that there is actually a formula for calculating your child’s approximate bladder capacity! According to —the Children’s Bowel & Bladder Charity—the formula for calculating bladder capacity is:

 Age of child x 30 + 30 = average bladder capacity in millilitres.

As an example, if you were calculating the balder capacity of a 6-year-old child, you would calculate it as follows: 6 x 30 + 30 = 210 millilitres (or 0.2 litres). Who knew something so small could be so pesky?

Of course, this figure is an average. Every child is unique! So, if your child is substantially smaller or bigger than other children their age, their bladder capacity’s likely to differ too. Either way, it’s reassuring to know that our Brolly Sheets hold up to 2 litres, so they’ll never let you down.


Make your journey to a dry night easy with Brolly Sheets 

We know that as a parent of a child who wets the bed it can be really hard to get some straightforward facts. We hope this helps! If you do notice unusual bladder capacity in your child, it’s easy to have a chat with your family doctor. But for most of you, now you know what “normal” is, you can at least put that nagging worry to rest.


After some more advice? Check out our Resources page for a collection of free toilet training guides