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 |
|---|---|---|---|---|
| Nutcase Baby Nutty | 47–50 (one size) | MIPS | 1 and older | not published |
| Giro Scamp MIPS II | XS 45–49 · S 49–53 | MIPS | XS: 1+ · S: 5+ | not published |
| Nutcase Little Nutty | Toddler 48–52 · Youth 52–56 | 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. 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 Nutcase Little Nutty Toddler (48–52), 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.
The picks
Every figure below is the manufacturer's own published spec, linked to the page we read it from. We have not ridden these bikes and the cards say so — here is how we choose.
Quick picks — sorted by head size
| # | Product | Best for | Head | Price |
|---|---|---|---|---|
| 1 | 45–53 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. | Toddlers and preschoolers | 45–53 cm | |
| 2 | 47–57 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. | School-age riders | 47–57 cm | |
| 3 | 48–56 Nutcase Little Nutty MIPS Toddler (48–52 cm) and Youth (52–56 cm) sizes with MIPS, in the graphics kids actually agree to wear — which is most of the battle. | The helmet they'll actually wear | 48–56 cm |
n/p = the manufacturer does not publish that figure. We do not fill in a number they never gave.
Top pick — Toddlers and preschoolers
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 |
What works
- 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
What doesn't
- MIPS versions cost more than the plain shell
- Dial fit systems can loosen and need re-checking
Hands-on status: Researched from published specs · Giro — Scamp MIPS II
#2 — School-age riders
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 |
What works
- 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
What doesn't
- CPSC certified for age 5 and older, so it is not a toddler helmet
- Universal sizing is less precise than two distinct shells
Hands-on status: Researched from published specs · Bell — Sidetrack II MIPS
#3 — The helmet they'll actually wear
Nutcase Little Nutty MIPS
Toddler (48–52 cm) and Youth (52–56 cm) sizes with MIPS, in the graphics kids actually agree to wear — which is most of the battle.
| Head size | 48–56 cm |
|---|---|
| Brakes | — |
| Frame | Hard outer shell, crumple-zone EPS, MIPS liner |
| Brand says | Complies with CPSC 16 CFR 1203 |
What works
- Two sizes cover 48–56 cm
- MIPS across the range
- Designs kids pick themselves, so it gets worn
What doesn't
- Skate-style shell runs warmer than a vented road shape
- Heavier than an in-mold helmet
Hands-on status: Researched from published specs · Nutcase — Little Nutty MIPS
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.
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.