Helmets & Gear
Kids helmet size chart
Helmet sizes are head circumference, measured in centimeters about an inch above the eyebrows. Toddler sizes run roughly 45 to 50 cm, child sizes 48 to 54, and youth sizes 50 to 57. Age bands are a rough guide only.
| Size | Head (cm) | Head (in) | Age it usually lands on |
|---|---|---|---|
| Toddler / XS | 45–50 | 17.7–19.7 | 1 – 3 |
| Small / Child | 48–54 | 18.9–21.3 | 3 – 7 |
| Youth | 50–57 | 19.7–22.4 | 7 – 12 |
Measure with a soft tape around the head, about an inch above the eyebrows. Sizes come from Giro, Bell, Nutcase and Lazer published charts.
Measure first: a soft tape around the head, level, about an inch above the eyebrows and above the ears. Round up to the nearest half centimeter. That single number selects the helmet.
Manufacturer sizes, actual figures
| Helmet | Sizes (head cm) | Rotational system | CPSC age | Weight |
|---|---|---|---|---|
| Giro Tremor MIPS | 47–54 (Universal Child) | MIPS | Child fit | not published |
| Giro Scamp MIPS II | XS 45–49 · S 49–53 | MIPS | XS: 1+ · S: 5+ | not published |
| NÜDL Youth MIPS | YS 52–55 · YM 56–60 | MIPS | 16 CFR 1203 | not published |
| Bell Sidetrack II MIPS | Child 47–54 · Youth 50–57 | Mips Evolve | 5 and older | 320 g (size Y) |
| Lazer Nutz KinetiCore | 50–56 (one size) | KinetiCore | 5 and up | 250 g |
Read from each manufacturer's published information on 2026-09-23, re-checked against the live listings on 2026-10-03. Where a brand does not publish a weight, we leave it blank rather than estimating.
Note how much the bands overlap. A 50 cm head fits a Giro Scamp S (49–53), a Giro Tremor MIPS (47–54), a Bell Sidetrack II Child (47–54) and a Lazer Nutz (50–56). At the overlap, choose on weight, ventilation and which one your child will wear.
Why age bands are unreliable here
Head circumference grows fast early and then slows dramatically. Two five-year-olds can be three centimeters apart, which is a whole size. Any chart that maps helmet size to age — including the age column in ours — is a starting point, not an answer.
Between two sizes?
Take the smaller one, provided the dial fit system closes comfortably. A helmet at the top of its range with the dial fully tightened has no adjustment left; a helmet at the bottom of its range has room to grow.
What to do after it arrives
Fit it properly before the first ride — the two-finger rule, the V under the ear, and the one-finger strap check are on how to fit a kids bike helmet. A correctly sized helmet worn badly is a badly fitted helmet.
For children under about five, where the certification wording changes between sizes in the same range, there is a dedicated toddler helmet size chart.
The picks
Every figure below is the manufacturer's own published spec, linked to the page we read it from, so you can check the one number your decision turns on — here is how we choose.
Quick picks — sorted by head size
| # | Product | Score | Best for | Head | Price |
|---|---|---|---|---|---|
| 1 |  Top pickGiro Scamp MIPS II The XS covers a 45–49 cm head and carries the CPSC certification for age 1 and up with extended rear coverage — the combination most toddler helmets miss. | 9.8/10 | Toddlers and preschoolers | 45–53 cm | |
| 2 |  Bell Sidetrack II MIPS 320 g in youth size with a visor and Mips Evolve — the value pick once a child is past five and riding further than the driveway. | 9.5/10 | School-age riders | 47–57 cm | |
| 3 |  NÜDL Youth MIPS A skate-shape helmet with MIPS inside and a magnetic buckle outside, in graphics kids pick for themselves — which is most of the battle at this age. | 9.5/10 | The helmet they'll actually wear | 52–60 cm |
n/p = the manufacturer does not publish that figure. Every other spec number here comes straight off their spec page. Scores are ours, on the 8.4–9.8 scale explained on our how we choose page.
Top pick — Toddlers and preschoolers
Category-defining · our scale
Giro Scamp MIPS II
The XS covers a 45–49 cm head and carries the CPSC certification for age 1 and up with extended rear coverage — the combination most toddler helmets miss.
| Head size | 45–53 cm |
|---|---|
| Brakes | — |
| Frame | In-mold polycarbonate shell, MIPS liner |
| Brand says | XS is CPSC certified for age 1 and older; S for age 5 and older |
Why we picked it
- XS 45–49 cm, S 49–53 cm — two sizes across the whole toddler-to-kid range
- Extended rear coverage on the XS
- Roc Loc Jr. dial fit with a pinch-guard buckle
Good to knowThe MIPS version costs more than the plain shell, and the dial fit wants a quick re-check at the start of each ride.
How we checked it: Researched from published specs · Giro — Scamp MIPS II
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#2 — School-age riders
Category-defining · our scale
Bell Sidetrack II MIPS
320 g in youth size with a visor and Mips Evolve — the value pick once a child is past five and riding further than the driveway.
| Head size | 47–57 cm |
|---|---|
| Brakes | — |
| Frame | In-mold polycarbonate shell, Mips Evolve |
| Brand says | CPSC certified for age 5 and older |
Why we picked it
- Universal Child 47–54 cm and Universal Youth 50–57 cm
- 320 g in size Y, light for a helmet with rotational protection
- Removable visor for trail riding
Good to knowCertified for age 5 and up on universal sizing, so it is the youth pick here rather than the toddler one.
How we checked it: Researched from published specs · Bell — Sidetrack II MIPS
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#3 — The helmet they'll actually wear
Category-defining · our scale
NÜDL Youth MIPS
A skate-shape helmet with MIPS inside and a magnetic buckle outside, in graphics kids pick for themselves — which is most of the battle at this age.
| Head size | 52–60 cm |
|---|---|
| Brakes | — |
| Frame | ABS skate-style shell over EPS, with a MIPS liner |
| Brand says | Two youth sizes: YS 52–55 cm and YM 56–60 cm |
Why we picked it
- MIPS in a bucket/skate shell, which most skate-style helmets skip
- Fidlock magnetic buckle: one-handed, and it cannot pinch a chin
- PAS dial fit system for a precise final adjustment
- 11 vents, which a skate shell usually does not have
Good to knowSizing starts at 52 cm, so this is a youth helmet rather than a toddler one, and a skate shell runs warmer than a vented road shape.
How we checked it: Researched from published specs · NÜDL — Youth MIPS helmet
#ad · How we make money · Price as of November 12, 2026
Questions parents actually ask
01How do I measure my child's head for a helmet?
Wrap a soft tape around the head about an inch above the eyebrows and above the ears, keeping it level. That circumference in centimeters is the helmet size.
02What size helmet for a 2 year old?
Usually 47 to 50 cm, which is the toddler band. Measure rather than assuming — head size varies a lot at this age.
03What size helmet for a 5 year old?
Most five-year-olds land between 50 and 54 cm, in the child or small youth band. A tape measure settles it in thirty seconds.
04Should I size up a helmet so it lasts?
No. A loose helmet rotates on impact and can come off. Buy the size that fits now and use the dial system for the growth you get within that range.
Our recommendation
Top pick
9.8/10Giro Scamp MIPS II
Toddlers and preschoolers. The MIPS version costs more than the plain shell, and the dial fit wants a quick re-check at the start of each ride.
#ad · How we make money · Price as of November 12, 2026
Runner-up
9.5/10Bell Sidetrack II MIPS
School-age riders. Certified for age 5 and up on universal sizing, so it is the youth pick here rather than the toddler one.
#ad · How we make money · Price as of November 12, 2026
Sources
Read next
- Helmets & GearHow to fit a kids bike helmetFour steps, two minutes, and the shake test that proves it.
- Helmets & GearBest kids bike helmetsFive helmets, compared on head size and certification.
- Helmets & GearBest toddler bike helmetsHelmets certified for age 1+, with the extra coverage required.
- Helmets & GearMIPS helmets explainedWhat the slip layer does, and when it is worth paying for.
- Helmets & GearBest kids bike helmets with MIPSThe four helmets here with a real MIPS liner, sized by head.