Baby hat sizes: size chart by age and head circumference
A hat that slips over your baby's eyes or is too snug usually means the size was guessed from the age, not measured. But finding out the right size isn't hard: baby hat sizes are simply head circumference in centimetres, and in the first year that figure changes fast. This guide walks you through measuring, the size chart and getting the fit right as your baby grows.
The essentials at a glance
Head circumference decides the size, not the age: it is more reliable than an age label as babies grow at different speeds.
Measure first, then read the chart: match the figure to the size column to find out the right size.
Size up between two sizes: the larger one leaves room to grow.
Newborn heads start at around 34 to 35 cm, but you need to re-measure often while their heads grow fastest.
Baby hat size chart by age and head circumference
Baby hat sizes work by head circumference in centimetres; the age column is only a rough guide, because babies grow at their own pace. To find out your baby’s size, measure the head, then read across to the size that matches the figure. If your figure sits between two rows, pick the larger size for a little room to grow.
Hat size | Age guide | Head circumference |
32/33 | 0–1 month (often for premature babies) | 32–33 cm |
34/35 | 0–1 month (often for premature babies) | 34–35 cm |
36/37 | 0–1 month (often for premature babies) | 36–37 cm |
38/39 | 0–1 month | 38–39 cm |
40/41 | 0–1 month | 40–41 cm |
42/43 | 2–3 months | 42–43 cm |
44/45 | 3–6 months | 44–45 cm |
46/47 | 6–9 months | 46–47 cm |
48/49 | 9–12 months | 48–49 cm |
50/51 | 1–2 years | 50–51 cm |
52/53 | 1–2 years | 52–53 cm |
Baby hat size guide: measuring your child's head
The whole baby hat size guide rests on one measurement, and it takes less than a minute. Use a soft tape measure, with your baby calm and still, and measure around the widest part of the head.
Hold the tape against the forehead, just above the eyebrows.
Run it around the widest part of the head, above the ears and around the back.
Draw the tape snug but not tight, then read off the figure in centimetres.
No tape to hand? Wrap a piece of string around your baby’s head along the same line, mark where it meets, then hold it against a ruler.
Tip: Measure twice and use the larger reading, so a slipped tape does not give you a figure that is too small.
Newborn hat size: what to expect for the smallest heads
A newborn's head is small—but only for a short while, because they grow quickly. The sizes 38/39 and 40/41 fit many newborns in the beginning, with the very smallest rows of the baby hat size chart reserved for tinier heads: premature babies usually fall below the standard newborn range, so the sizes 32/33, 34/35 and 36/37 are often used for premature babies.
The head size you measure at birth steers the first hats, but the smallest sizes fit only briefly. It’s definitely worth checking the figure again within the first few weeks as the smallest sizes are outgrown quickly.
From baby to toddler and the right fit
Head circumference rises quickly in the first year and then slows noticeably, so from around age two, you have to replace hats far less often than in the early months. For older children, makers vary: some size by head circumference, some by age, some by body height, so this chart pairs body height, an age guide and head circumference.
Body height | Age guide | Head circumference |
92-104 cm | 2-4 years | 48.5-50 cm |
110-122 cm | 4-7 years | 50.5-51.5 cm |
128-140 cm | 7-10 years | 52-54 cm |
146-158 cm | 10-13 years | 54.5-55.5 cm |
The method never changes: the head circumference at the widest part is the figure that matters. Beyond size, check the fit: a good hat sits snug enough not to slip but never tight, sits just above the eyebrows, and leaves no red marks. Give the hat a gentle tug; if it slides, it is too big.
Why a well-fitting hat matters for your baby
A hat is more than a finishing touch for a cute outfit. Newborns cannot regulate their own temperature, and most heat loss happens via the head, so a hat that fits keeps the head and ears warm when it is cool.
In summer a hat works the other way around. A wide-brimmed hat shades the face, neck and ears from the sun, as babies under six months are best kept out of direct strong sunlight. But don’t worry: Baby hat sizes stay the same across the year, so it is the fabric and the brim that change, not the centimetre figure.
Conclusion: measure the head and the size follows
Once you treat the head circumference as the answer, baby hat sizes stop being a guess. Measure the widest part of the head, match the centimetre figure to the chart, and size up if you land between two rows. Re-measure before each new hat while your baby’s head grows fastest, then less often as your child gets older.
FAQs about baby hat sizes
How often should you re-measure a baby's head?
Re-measure before you buy a new hat, and check more often in roughly the first six months, when the head grows fastest. Head circumference increases on average about 1 cm a month across the first year, so a hat that fit a few weeks ago can already be snug a little while later.
What size is a 0-3 month or newborn hat?
A newborn or 0-3 month hat covers roughly a 35 to 40 cm head circumference, depending on the head you measure. Premature babies start below that range, so the smallest sizes suit them. Measuring is still the safest way to land on the right size.
Sources
https://www.c-and-a.com/eu/en/shop/service/products-stock/size-guide (accessed on 22.06.2026)
https://www.merckmanuals.com/professional/pediatrics/growth-and-development/physical-growth-of-infants-and-children (accessed on 22.06.2026)
https://www.nhs.uk/conditions/baby/caring-for-a-newborn/reduce-the-risk-of-sudden-infant-death-syndrome/ (accessed on 22.06.2026)
http://www.craftyarncouncil.com/headsize.html (accessed on 22.06.2026)
https://www.nhs.uk/conditions/baby/babys-development/height-weight-and-reviews/baby-reviews/ (accessed on 22.06.2026)
https://www.stgeorges.nhs.uk/wp-content/uploads/2025/03/MAT_KBW.pdf (accessed on 22.06.2026)
https://www.nhs.uk/live-well/seasonal-health/sunscreen-and-sun-safety/ (accessed on 22.06.2026)
Image sources in chronological order in the text
Cover image: stock.adobe.com/Bostan Natalia
1st image in text: stock.adobe.com/Pixel-Shot
2nd image in text: stock.adobe.com/blackday
Third image in text: stock.adobe.com/leungchopan