Rule
The same published rule as adults: head circumference in inches ÷ π = fitted size, rounded to the nearest 1/8. Nothing about children's heads changes the maths.
Children · babies · toddlers
Kids' hat size chart
Children's hats are sized by head circumference, not age. The age bands below are only population medians (sourced from WHO and CDC growth standards) — two healthy children of the same age can differ by several centimetres. Measure the head, then use the tables. This youth hat size chart runs from newborn to the adult-size bridge at 53 cm.
| Age | Typical head circumference (cm) | Note |
|---|---|---|
| Birth | 33.9–34.5 cm (13.3–13.6 in) | preemie and newborn hats are sold by these ranges |
| 3 months | 40.2–41.1 cm (15.8–16.2 in) | |
| 6 months | 42.2–43.3 cm (16.6–17.0 in) | |
| 12 months | 44.9–46.1 cm (17.7–18.1 in) | |
| 18 months | 46–47 cm (18.1–18.5 in) | |
| 2 years | 46.7–47.8 cm (18.4–18.8 in) | |
| 3 years | 47.6–48.7 cm (18.7–19.2 in) | |
| 4 years | 48.2–49.2 cm (19.0–19.4 in) | |
| 5 years | 48.9–49.9 cm (19.3–19.6 in) | |
| 6 years | 49.3–50.3 cm (19.4–19.8 in) | |
| 8 years | 50.2–51.3 cm (19.8–20.2 in) | |
| 10 years | 51.1–52.2 cm (20.1–20.6 in) |
Age bands are population medians, not targets. Measure the child's head and fit by the measured size; ages only tell you which range is typical. Healthy children of the same age can differ by several centimetres.
| US | Head (cm) | Head (inches) |
|---|---|---|
| 6 | 47.9 | 18 7/8 |
| 6 1/8 | 48.9 | 19 1/4 |
| 6 1/4 | 49.9 | 19 5/8 |
| 6 3/8 | 50.9 | 20 |
| 6 1/2 | 51.9 | 20 3/8 |
From 53.0 cm (US 6 5/8) upward, use the adult hat size chart.
How to convert a child's head measurement
Examples
A 47.9 cm head (18 7/8 in) takes a US 6. A 51.9 cm head (20 3/8 in) takes US 6 1/2. Adult sizes start at 53.0 cm (US 6 5/8) — most children reach that between 6 and 10 years.
In practice
Most children's hats are sold as knits with stretch (“0–6 months”, “2–4 years”) rather than fitted sizes — treat those labels as ranges that must be verified against the measurement.
Where these numbers come from
- Age bands — WHO Child Growth Standards, head circumference-for-age, 50th percentile (who.int/tools/child-growth-standards) from birth to 5 years; CDC growth charts for 5–10 years.
- Fitted sizes — derived with the published conversion rule above (mechanical, not a brand chart).
- Checked 2026-10-21. Children's head sizes are individual — these tables are medians, not a fit guarantee.
Kids' hat size FAQs
What is the average head circumference of a newborn?
Around 34–35 cm for a full-term baby — WHO standards put the median at 34.5 cm for boys and 33.9 cm for girls. Newborn hats are cut for exactly this span, which is why a “0–3 months” hat is really a head-size claim, not a calendar claim.
How fast do children's heads grow?
Very fast at first: roughly 1 cm per month in the first three months, then slowing to about 1 cm every two months until the first birthday. After that, growth decelerates sharply — a hat bought at 18 months may still fit at two years.
Can I use the adult hat size chart for my child?
Yes, once the head measures at least 53.0 cm — usually between 5 and 10 years. The fitted sizes below 53 cm run on the same system (head in inches ÷ π), just smaller: US 6 to 6 1/2 covers the youngest heads that wear fitted caps.
How should a children's hat fit?
Children rarely tolerate tight, so most children's hats are knits with give or adjustable-closure designs rather than fitted caps. Measure the head, buy to the measurement, and check the fit every season — a hat that is merely snug today will be too small next month.
Why do you show ages at all, if measuring matters more?
Because buyers search by age and gift-givers need a starting point. The age bands here are population medians from WHO/CDC data — a typical range, not a rule. The headline advice everywhere on this page is the same: measure the child's head.