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How to find the right size baby clothes

It’s never easy finding the right size in clothing, and baby clothes are no different. Just like adult clothing each brand has their own interpretation of the size. In the UK baby clothes are typically sold by their age, and there are at least 6 sizes starting from newborn up to 24 months.

Each size corresponds with a particular height, but of course, like adults, babies of a particular age are all different shapes, weights and heights. So searching for baby clothes to fit by age isn’t ideal. A much better measure is the height, and for infant babies the weight.

Some brands split size 6-12 months into two sizes, 6-9 months size (Height 74cm) and 9-12 months (Height 80cm).

How brands establish the best sizing for their customer

The last published data on baby sizes was from the British Standards Institute (BSI) in 1990, and the standard was developed from a set of measurements collected in 1978! So with today’s greater knowledge of baby health and welfare, babies, like adults, will have no doubt changed in average size and shape in the last 40 years.

So it’s no wonder the sizing is so variable between brands. To determine what sizing should be adopted, in view of the lack of current sizing data, brands will carry out competitive shops. This is when the brand will buy the same styles from their competitors, to see how they compare against their competitors sizing. Some brands use their suppliers to determine the sizing for their ranges.

Using competitor shopping, fittings on actual babies, and customer feedback, baby clothing brands have continued to improve and upgrade their own sizing measurements.

Using height to buy the right size baby clothes

Age, weight and height are the three parameters that are considered when buying baby clothes. While it might be better to get your baby clothes based on the height, it’s not always possible to measure your very fast growing baby every time you want to buy something. But recognising the height used for each ‘age’ size will go a long way in getting the right fitting clothes for your baby. In the early months your baby will be weighed and their length (height) taken during visits to the doctor or healthcare professional, but when these visits are less, it would be good to know how to measure your baby yourself.

Top tip: Baby clothes sized as 6-12 months are more aligned with the 9-12 months size and are generally too big for babies that normally wear the 6-9 months size. This makes sense as the Height measurement for 6-12 month and 9-12 months are both 80cm.

The same applies to baby clothes like puddlesuits that have a 0-6 month size, there is no way they will fit a baby that is at the smaller end of this size range, and the Height measurement given is 68cm which is the actually the 3-6 month size. In fact because a puddlesuit is designed to fit over other clothes, it may even be too generous for a lean baby.

There’s a more lee-way with baby items like sleeping bags, which are sized 0-6m, 6-18m and 18-36m, as long as the baby’s head and arms are securely outside the sleep bag, the length of the bag allows plenty of room for fast growing babies.

How to measure your baby’s size for clothes

The best way is to lay your baby on a flat surface, already marked out with a height measure. You need to measure from the top of the head to the heel, with your baby’s legs gently pulled out to straighten them to get an accurate height. Because your baby will probably be wriggling, it’s best to do this with help from another person.

As your baby grows and is able to walk, you can take their height by standing them with their back against a wall, and taking the height by measuring from the top of the head to the floor.

True to size

You may think that a good indicator of the fit of a brand is to look at their customer reviews. Some brands even ask their customers to rate whether their fit is ‘True to size’. But what does this actually mean? The size measurement stated by the brand will either be the maximum measurement for that size, eg 68cm, or a size height range will be indicated eg 62-68cm. Where a size height range is given True to size could mean that the fit is targeted at the middle of the size height range. So for a height range of 62-68cm it will be targeted at height 65cm. But sometimes brands will target the top end of the size height range as this will allow the baby clothes to be worn for longer, this will usually mean that the clothes will be longer in the body and legs. And it is not a given that if a maximum size height measurement is stated, that the fit will be targeted at that height.

The 75th percentile

There is something called the 75th percentile. Some brands work on the basis that their sizing should fit the 75th percentile, but rarely is this stated, and what does it mean? The 75th percentile is a value given for weight and height and it refers to how your baby compares to 100 babies of the same age. If your baby is in the 75th percentile for height, it means that your baby is the same height or taller than 75% of the other babies. So clothing that is sized to fit the 75th percentile will be more generously sized than clothing sized to fit the 50th percentile. The British Standard sizing data gives a range of sizing values for each percentile which brands can use to base their sizing on. They can combine this information with their findings from competitor shopping, fitting their clothes on babies and customer feedback.

If you choose different brands, and one has a different height for the same size than another brand you have selected, there will probably be a difference in the fit of the baby clothes, and one may appear bigger than the other.

Other factors affecting the fit of baby clothes

There are lots of other reasons why there is a variation in how clothes fit your baby. They should all be considered when buying clothes. Fit of clothing is a balance between aesthetics and comfort.

End Use

You probably would expect two different styles, from the same brand, in the same size to fit your baby. End use of the clothes plays a big part in whether the clothes fit your baby in a particular size.

For example a baby sleepsuit will fit closer to the body, than an all in one puddlesuit which is designed to fit over other clothes. The sleepsuit may fit your baby until he or she has grown to the maximum height on the label. Because the puddlesuit is looser, it can be worn for longer as it will have more fabric in the length and width to accommodate clothing layers.

close fitting baby clothes
rainbow baby snowsuit


Some styles are designed to fit closer to the body, while others are designed to be looser. For example baby leggings are made in a soft knitted fabric and will be worn closer to the body. Woven trousers are designed with a wider leg and elasticated or ribbed waist. Both are comfortable. But as your baby grows the closer fitting leggings will soon become too snug and uncomfortable. They will be outgrown quicker than the looser trousers.


Winter and summer styles also have a different fit. A winter baby jacket will be padded and may even be fleece lined. It will also be designed to be worn over different layers. A spring or summer baby jacket will be made from a lighter fabric with less layers in the jacket. It will be designed to worn over thinner clothes and will have a smaller fit than the bulkier winter jacket.


The materials used to make the baby clothes play an important part in the fit of the clothes. They also impact on how long your baby can continue to wear the clothes. A soft dress in a knitted fabric will have a bit of stretch, compared to a woven dress. The knitted dress will expand to a degree as your baby grows and can be worn for longer. Your baby will outgrow the woven dress quicker. Due to the rigidity of the woven fabric the dress will not be able to expand as your baby grows.


Fibres with less stretch are more likely to be found in clothes that are bigger. This is to allow for ‘ease’ in the clothing.


‘Ease’ is an allowance included in a garment which allows for the clothes to be put on comfortably without restriction. Less ‘ease’ means there is less room in the clothes to manoeuvre your baby in and out of.

Manufacturing tolerance

This is the allowance permitted when factories have made the clothes. A tolerance could be plus or minus either side of a specific measurement. The result is that you could have a bigger or smaller fitting garment in the same label size.

Getting the right size baby clothes

Often parents will buy a bigger size because babies grow so fast. An advantage of renting baby clothes is that you can rent the size your baby is. The clothes are simply returned when your baby has outgrown them. Renting clothes also reduces waste and prevents discarded baby clothes ending up in landfill. The rental service will maintain and care for the clothes so they can be kept in circulation longer while maintaining a premium condition.

Qookeee brands

Having worked with several baby brands we can see that there can be a difference in the height stated for certain sizes, and less variation on others, so checking the size chart first is the best starting point. The biggest variation seems to be on the Newborn and 0-3m size. The height ranges of the different brands are much closer on the other sizes. We’re working on a fit guide so you rent the right size baby clothes when you’re renting.

When putting our baby bundles together we always choose brands and products that are similar in sizing. We often make up the bundle with clothing from one brand.