Baby clothes sizes: how to find the right fit by age
The size on the label and your baby's age rarely line up, and that mismatch is what trips most parents up. Two babies born on the same day can need different baby clothes sizes, because length, not age, is what really counts. Get that one idea straight and this guide shows you the rest, from reading the chart to measuring and knowing when to size up.
The essentials at a glance
Length, not age, decides: the size number matches your baby's body length in centimetres, so measure first.
Dual labels buy time: a 50/56 garment is cut to the larger figure, so it fits for weeks.
Between sizes, go bigger: the larger size leaves room to grow and saves a return.
Newborn passes fast: most babies only wear the smallest size for a few weeks, so buy a small starter set.
Shoes and hats differ: these go by foot length or head circumference, not the clothing chart.
Baby size chart by age and month
Baby clothing follows body length in centimetres, so the size number is roughly your baby's height. Size 56 fits a baby up to about 56 centimetres long, size 62 up to 62 centimetres, and so on in six-centimetre steps. For tops, bottoms and all-in-ones, the chest and hip figures matter too.
Size | Age guide | Body length (cm) | Chest (cm) | Hip (cm) |
|---|---|---|---|---|
42–46 | 0–1 month | up to 46 | up to 36 | up to 34 |
50 | 0–1 month | around 50 | 36 | 34 |
56 | 0–1 month | 51-56 | 38.5 | 37 |
62 | 2–3 months | 57-62 | 43 | 42 |
68 | 3–6 months | 63-68 | 45.5 | 45 |
74 | 6–9 months | 69-74 | 47 | 47.5 |
80 | 9–12 months | 75-80 | 49 | 50 |
86 | 12–18 months | 81-86 | 51 | 51 |
92 | 18–24 months | 87-92 | 52.5 | 53 |
The smallest sizes turn over quickly. A newborn may move through 56 and 62 within the first weeks, while the larger sizes settle in for several months as growth slows. When a measurement lands between two rows, round up: a size that is a touch generous is far easier to live with than one already tight at the shoulders.
How do baby clothes sizes work? A baby size guide
This baby size guide rests on three ideas: the number on the label is a body length in centimetres, the age band is only an estimate, and combined labels cover a wider stretch of growth. Start with the first, since it does most of the work: a baby of 60 centimetres sits in size 62, the next step up from 56.
What a combined label like 50/56 means
Some garments carry two numbers, such as 50/56 or 62/68. The piece is cut to the larger of the two sizes, so a 50/56 romper has the dimensions of size 56 and suits a baby up to about 56 centimetres. It fits smaller babies with room to spare, so it stays wearable for weeks rather than days, which is handy in the fast-growing early months.
Why the age on the label is only a guide
Age recommendations give baby sizes an everyday reference, but babies do not all grow at the same pace, so two born on the same day can sit a size apart. When the age and the measured length disagree, follow the length, and let the fit of clothes your baby already wears tell you when the next size is due.
Tip: Keep a soft tape measure in the changing bag and jot down the figure each time, so the age column never has to decide for you.
Newborn clothes: weight, size and how long they fit
So what size are newborn clothes? It is simply the smallest and briefest stage on the chart, sitting in the shortest-length rows above. Most babies pass through these newborn-sized clothes within the first few weeks, so a small starter set beats a large newborn haul.
Weight is a useful cross-check for that first size. A newborn size suits babies of about 2 to 5 kilograms, the same band used for the smallest nappies, so the newborn clothes weight band confirms your choice when a measurement lands on a boundary. For a dedicated newborn size chart, read the smallest rows by length, then check that weight.
Tip: Hold off on buying lots of newborn clothes before the birth. Buy a small starter set, then top up with the next size as your baby grows.
Baby clothes sizes: UK and EU sizing explained
This is where confusion usually starts: some labels show a centimetre size, others a UK-style age band such as "0-3 months". The centimetre number names your baby's body length precisely, while an age band only estimates when it tends to fit.
The measurement reconciles the two: measure once, then find that length on the chart above. The chart pairs size 56 with the 0-1 month guide and size 68 with the 3-6 month guide, so your baby's length points to the right band whichever system a retailer prints.
How to measure your baby and when to size up
Three measurements are all you need, as the chart above shows:
Body length: take it with your baby lying flat and measure from the crown of the head to the heel, with legs gently straightened.
Chest: measure around the fullest part of the chest, just under the arms.
Hip: measure around the widest part of the bottom and hips, leaving room for the nappy.
After the first month, a baby grows by about 2.5 to 3 centimetres a month, and by around 25 centimetres over the first year. That crosses a six-centimetre size step in roughly two months, so expect to size up every one to two months at first. When your measurement lands between two sizes, choose the larger one. The bigger size leaves room to grow, which matters when a snug fit can be outgrown within a fortnight.
Shoes and socks follow their own scale, set by foot length:
Shoe/sock size | Age guide | Body length (cm) | Foot length (cm) |
10/11 | 0-3 months | up to 44 | 6.5 |
12/13 | 0-3 months | 44-50 | 6.5 |
14/15 | 0-3 months | 56-62 | 8 |
15/17 | 3-9 months | 68-74 | 10 |
18/20 | 9-18 months | 80-86 | 12 |
21/23 | 1.5-3 years | 92-98 | 13 |
24/26 | 3-4 years | 98-104 | 15 |
Tip: re-measure your baby every few weeks in the first year, when growth comes in spurts, so you switch to the next size before clothes start to pull.
How many baby clothes do you need in each size?
Once you can read baby clothes sizes off the chart, the smallest sizes are worn for only a few weeks, so buy light at the bottom and more generously higher up.
A simple first-weeks set is smaller than many expect: around 6 all-in-one stretch suits or sleepsuits, 6 vests or bodysuits, and 2 cardigans, plus a hat, mittens and socks for cold days out.
Newborn and size 56: a small starter set, since this stage passes in weeks.
Sizes 62 and 68: more pieces here, as these tend to be worn for two to three months each.
Size 74 and up: a fuller set, because growth slows and each size lasts.
For more detail on quantities, our guide on how much clothing a newborn needs has a full checklist.
Conclusion: Go by length and the rest follows
Baby clothes sizes look fiddly at first, but it comes down to one habit: measure your baby's length, read it across the chart, and treat the age band as a guide. Combined labels like 50/56 buy extra weeks, and sizing up leaves room. Keep a fresh measurement to hand and you will pick the right size every time.
FAQs about baby clothes sizes
What size should I buy for a newborn baby?
Start at the smallest length rows on the chart, around sizes 50 to 56 for a baby of roughly 2 to 5 kilograms. Measure your baby's length and read across, using weight as a cross-check. Buy only a small starter set, because most babies move up within weeks.
How long do babies wear newborn size clothes?
Newborn clothes are the smallest size on the chart, and they tend to fit for only a few weeks. Babies grow very quickly early on, so keep the next size up ready to switch.
What size does a baby need at each age?
As a rough guide, newborns to one month sit around sizes 50 to 56, two to three months around 62, three to six months around 68, six to nine months around 74, and nine to twelve months around 80. These are averages only, so measure and read across the chart.
Can you go by your baby's weight instead of length?
Weight works well as a cross-check. The clothing chart itself is built around body length though, so length stays the main guide when a measurement sits on a boundary.
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Sources
https://www.c-and-a.com/eu/en/shop/service/products-stock/size-guide (accessed on 22.06.2026)
https://www.msdmanuals.com/home/children-s-health-issues/growth-and-development/physical-growth-of-infants-and-children (accessed on 22.06.2026)
https://www2.hse.ie/babies-children/checks-milestones/physical-development/length/ (accessed on 22.06.2026)
https://www.nhs.uk/baby/caring-for-a-newborn/what-you-will-need-for-your-baby/ (accessed on 22.06.2026)
https://www.craftyarncouncil.com/standards/baby-size-chart (accessed on 22.06.2026)
https://www.pampers.co.uk/safety-and-commitment/nappies-and-wipes/article/pampers-nappy-size-and-type-guide (accessed on 22.06.2026)
Image sources in chronological order in the text
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1st image in text: stock.adobe.com/Africa Studio
2nd image in text: stock.adobe.com/netrun78
3nd image in text: stock.adobe.com/epiximages