What Size Nappy for their Age

What Size Nappy for their Age

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Sadly, you can’t just pick any pack of nappies and call it a day. Choosing the correct nappy size for your baby isn’t an easy task. How do you know what size nappy for what age?

It can be a confusing experience trying to find the nappy fit that’s both most leak-free and most comfortable for your baby’s bottoms.

The danger is, and one I’ve seen a few times during my rounds as a health visitor on Merseyside is that a nappy that’s too small causes wee and poo to leak out all the time (don’t get me started on Poonamis) which leads to nappy rash, a nappy which is too tight can make them permanently uncomfortable and often chafing on the inner thigh.

chafing baby inner thigh
Effects of a nappy that’s too tight

In this post, we share the importance of getting the right nappy size and how to choose a nappy size for your little one. So, let’s get started!

Why Getting the Right Size Is Important


Getting the right nappy size is essential for your baby’s comfort. A well-fitting nappy will have good absorption and ventilation. It’ll keep your baby dry and comfortable while also preventing leaks. But, it shouldn’t be kept on for too long and you will still need a good changing mat.

A well-fitting nappy should be snug around your baby’s waist and thighs, but not so tight that it digs in and leaves red marks. In addition, there should be no gaps between the baby’s legs and the nappy.

A poorly fitting nappy, on the other hand, can be frustrating for your baby. If the nappy is too small, it can cause discomfort, blowouts (poonami), and rashes. Leakages can occur if the nappy is too large.

What Size Nappy Fits What Age?

Because no two babies weigh the same, it’s impossible to accurately determine a baby’s weight at what age. What’s more, there are some slight variations among nappy brands.

Nevertheless, you can use the following guideline as a general rule of thumb.


We haven’t put a finger in the air to get these recommendations. We’ve done two things – We have used the Royal College of Paediatrics and Child Health charts for boys and girls. Next, we used those numbers to get age ranges for weights and then lastly we’ve correlated the age ranges and weights with the weight recommendations from nappy brands size guides.

You can use this guide in two ways – if you know their weight then use the weight range data, if not then use the age.

Hope that makes sense.

Size 1

Ages: up to 16 weeks

Weight range: 2-5 kg

Often, size 1 nappies are designed to accommodate babies’ new, sensitive skin in the first few weeks and months. They’ll have terms such as ‘baby dry’ and ‘super dry’ on the package because staying dry and preventing nappy rashes is essential at this age.

Keep in mind that even the smallest nappies may be massive for premature babies. Some brands do offer nappies for babies with low birth weight, which are often referred to as size 0 or preemie diapers.

Size 2

Ages: up to 28 weeks

Weight range: 3-6 kg

Baby boys typically grow from size 1 to size 2 in about three to four months. Average-sized baby girls, on the other hand, may take a little longer, transitioning from size 1 to 2 between four and five months.

Size 3

Ages: up to 52 weeks

Weight range: 4-9 kg

Nappies in sizes 3 and up are designed to keep the baby comfortable while crawling and learning to move. On the package, you may see terms like ‘active fit’ and ‘active stretch.’

Size 4

Ages: 18 to 24 months

Weight range: 7-18 kg

Size 4 nappies are suitable for toddlers aged one and a half to four years. Toddlers around that age either grow quickly or gradually.

That’s why most parents find themselves unable to commit to stocking up on nappies at that age until they can determine their babies’ growth rate.

Size 5

size 5 nappy

Ages: Two to four years

Weight range: 11-25 kg

You may notice a weight and age overlap between this size and the previous one. The main distinction between them is the nappy’s overall physical size.

Size 6

Ages: Four years and up

Weight range: 16+ kg

Most babies don’t make it to size 6 nappies. At this age and weight, there’s a good chance your baby has mastered potty training and no longer requires nappies.

Size 7

Ages: Five years and up

Weight range: 17+ kg

Unless there’s a special reason, most toddlers will have been potty trained by the time they’re in size 6 nappies. That said, a chubby toddler who hasn’t yet been potty trained may grow into size 7 nappies.

Size 8

Ages: Over five years

Weight range: 19+ kg

Size 8 nappies are uncommon and are typically worn by eight to 10-year-olds weighing between 22 and 27 kg.

In most cases, children who wear size 8 nappies suffer from a medical condition that makes them unable to control their bladders or bowels.

In Conclusion

All in all, you should always be observant and pay attention to your baby. Depending on his or her growth rate, you may size up your baby’s nappies more or less frequently than the average toddler.

Just make sure that the nappy doesn’t leave red marks on your baby or cause leakage. You can also experiment with different brands, as you may find that one brand may work better than others for your baby.

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