Kids' Bike Helmet Sizing Guide UK 2026

DDuncan McGregor ·09 September 2026 ·8 min read

We build and safety-check every kids' bike that leaves our warehouse, and the one thing we can't check for you is the helmet. A helmet only works if it fits, and a surprising number of the ones we see on customers' children don't — too big, too far back, straps flapping. This guide covers how to measure a child's head, how to check the fit once it's on, when a helmet needs replacing, and which of the junior helmets we currently stock suits which head.

The short version: measure the head, don't guess from age. Then buy a helmet whose size range straddles that number, and spend two minutes adjusting it properly. Our junior picks start at £7.50 and the Alpina Ximo and Hackney are £19.99–£24.99, all at least 50% off RRP.

Measuring a child's head for a bike helmet with a tape measure above the eyebrows

How to measure your child's head

You need a soft tape measure (a dressmaker's tape, or a piece of string and a ruler will do).

Wrap the tape around the widest part of the head — about 2cm above the eyebrows at the front, above the ears, and around the bump at the back of the skull.
Keep it level and snug but not tight. Don't pull hair in under it.
Read the measurement in centimetres. Do it twice; kids wriggle.
Write it down. You'll want it again in six months.

That number is your child's head circumference, and every helmet on our site lists its range in centimetres in the title. If the measurement falls in the top centimetre of a helmet's range, go up a size — children's heads grow, and the adjustment dial can take a helmet smaller but not bigger.

Typical head sizes by age (a rough guide only)

Age	Typical circumference	Helmets we stock in this range
18 months – 3 years	roughly 45–49cm	Alpina Ximo 45–49cm, Wilkinsons Junior 46–53cm
3 – 5 years	roughly 47–51cm	Alpina Ximo 47–51cm, Alpina Hackney Junior 47–51cm
5 – 8 years	roughly 50–53cm	Wilkinsons Junior 46–53cm (top of range)
8+ years	52cm and up	Ask us — see the note on older kids below

These are averages and there is enormous variation, which is exactly why we tell you to measure. We've fitted three-year-olds who needed 51cm and seven-year-olds who were fine in 48cm.

The helmets we stock

Helmet	Size	Price (RRP)	Weight	Construction	Standard
Alpina Ximo LE, Green	47–51cm	£19.99 (£39.95)	—	Inmould, reflective stickers	EN 1078
Alpina Ximo Disney Star Wars	45–49cm	£22.49 (£49.95)	—	Inmould, ceramic shell, Hi-EPS, Run System Classic Slide	EN 1078
Alpina Ximo Disney Star Wars	47–51cm	£22.49 (£49.95)	—	As above	EN 1078
Alpina Ximo Disney Frozen	45–49cm	£22.49 (£49.95)	—	As above	EN 1078
Alpina Hackney Junior, Green Frog	47–51cm	£24.99 (£49.99)	210g	Inmould, ceramic shell, Hi-EPS, height-adjustable Run System	EN 1078
Junior Cycle Helmet, Blue (Wilkinsons)	46–53cm	£7.50 (£15.00)	—	Peak, vents, removable pads	EN 1078

The Alpina Ximo Disney Cars (45–49cm) is currently sold out. All prices correct at time of writing — check the product page.

Alpina Ximo: the toddler and pre-schooler helmet

The Ximo is Alpina's small-head helmet and it's designed with real thought for the under-fives. It's pulled extra low at the sides and back for coverage, the rear is flat so it doesn't push the child's head forward in a bike seat or trailer, the vents are angled so sun doesn't fall directly on the scalp, and the Ergomatic buckle is twist-proof with a multi-stage lock — you can do it up one-handed while the child squirms. The Disney versions add the ceramic three-layer shell, Hi-EPS core, Edge Protect around the rim and Run System Classic Slide dial for three-dimensional adjustment; the LE version is the plainer, cheaper take with reflective stickers.

Two sizes: 45–49cm (Frozen and one of the Star Wars) and 47–51cm (the other Star Wars and the LE Green). At £19.99–£22.49 against a £39.95–£49.95 RRP, they're the best-value quality helmets we've had for small heads in a long while.

Alpina Ximo Disney Frozen kids helmet showing the rear adjustment dial

Alpina Hackney Junior: the school-run helmet for 4–7s

The Hackney Junior is the more grown-up option for the 47–51cm head. It's a 210g inmould helmet with the ceramic shell thermally bonded to a Hi-EPS core, a height-adjustable Run System dial that also tilts to cup the back of the head, ear straps that adjust properly, the same twist-proof buckle, and a mounting point for Alpina's optional plug-in rear light. It's rated for city, tour, MTB and inline skating, so it'll do scooters and skate park as well as bikes. £24.99 against a £49.99 RRP; green frog colour.

Wilkinsons Junior: the £7.50 spare

Sometimes you need a helmet that lives at grandma's, or a backup for the child who's lost theirs the week before a holiday. The Wilkinsons Junior is EN 1078 certified, 46–53cm, with an aero peak, vents and removable pads, and it's £7.50. It won't have the Alpina's shell quality or adjustment, but a properly fitted £7.50 helmet beats a badly fitted £50 one, and it covers the 51–53cm heads the Alpinas don't.

A note on older kids (52cm and up)

At the time of writing our stock of junior helmets tops out at 53cm. The only bigger Alpina we have is the Comox MTB helmet at 57–62cm (£50, RRP £129.95), which is an adult large — fine for a bigger teenager, wrong for a nine-year-old. If your child measures 53–57cm, give us a call and we'll tell you what's just come in or point you somewhere honest.

The fit check: two minutes that matter

Once the helmet's on, run through this every time — kids' heads grow, straps loosen, and helmets get borrowed by siblings.

Position. The helmet should sit level, with the front edge one or two finger-widths above the eyebrows. Tipped back on the crown is the most common mistake we see and it leaves the forehead exposed.
Dial. Tighten the rear dial until the helmet stays put when the child shakes their head "no" with the straps undone. It shouldn't rock forward, back or side to side.
Side straps. The Y of each side strap should sit just under the earlobe, with the ear in the middle of the V.
Chin strap. Done up, you should be able to get one finger — not two — between the strap and the chin. The child should be able to open their mouth wide and feel the helmet pull down slightly.
Push test. Push the front edge up and back. If it moves more than an inch, tighten the dial and the front straps.

Ponytails go under the rear dial or through a port if the helmet has one, never bunched up inside. And no hats, hoods or headphones under the helmet — they stop it sitting on the head properly.

Checking a kids bike helmet fit with two fingers above the eyebrows and one under the chin strap

When to replace a helmet

After any crash where the helmet hit something. The EPS foam is designed to crush once. It may look fine; it isn't. This includes a fall off a scooter or a drop down the stairs onto a hard floor.
When it no longer fits. If the dial is fully out and it's still tight, or it sits above the eyebrows however you adjust it, it's done.
Every few years regardless. Sweat, sun and knocks degrade the foam and the shell. Most manufacturers suggest three to five years from purchase; for a kids' helmet that gets thrown in the shed, we'd be at the shorter end.
If the shell is cracked, the straps are frayed or the buckle doesn't lock positively.

Second-hand helmets are a genuine no. You can't see the history.

Matching a helmet to a bike

We're asked this every week, so here's the honest pairing for our own Shyre range. The head sizes are typical, not guaranteed — measure first.

Shyre bike	Age / height	Typical head size	Helmet we'd start with
Myndie 12 balance bike — £69.99	18mo–4yrs	45–49cm	Alpina Ximo 45–49cm (Frozen / Star Wars)
Hopton 16 — £279.99	4–6yrs, 100–120cm	47–51cm	Alpina Hackney Junior or Ximo 47–51cm
Hopton 20 — £319.99	6–8yrs	50–53cm	Wilkinsons Junior 46–53cm; Hackney if under 51cm
Eastie 20 — £339.99	6–9yrs, 115–135cm	50–53cm	As Hopton 20 — for trail use the Hackney's MTB rating is a plus
Hopton 24 — £339.99	8–11yrs	52–55cm	Call us — junior stock currently tops out at 53cm
Hopton 26 — £359.99	10–13+	54–58cm	Alpina Comox 57–62cm for bigger teens; otherwise call us

Add a helmet to your basket with a Shyre or any other kids' bike and it ships with free UK delivery. Helmets are covered by our 90-day no-quibble returns if the size is wrong, as long as it's unworn and unmarked; the bikes carry our 12-month warranty (lifetime on Shyre frames and forks).

Who is this for?

Good for: - Parents buying a first helmet for a balance bike or 16" pedal bike — the Ximo range is the best value we've had at 45–51cm - Kids who need a helmet for bike, scooter and skate park — the Hackney Junior is rated for all three - Anyone who wants a cheap, certified spare — Wilkinsons at £7.50

Not for: - Heads over 53cm, until more junior stock lands — ring us - Anyone hoping to hand a helmet down through three children (measure each one, replace after any knock)

Alternatives

Alpina Comox MTB helmet — £50 (RRP £129.95). 57–62cm, for bigger teenagers and adults.
Shop all Alpina helmets →
Shop the full Shyre range →

Final verdict

Measure the head, buy the helmet whose range covers it with room to grow, and spend two minutes on the dial and straps. For 45–49cm heads the Alpina Ximo at £22.49 is the one to buy; for 47–51cm the Hackney Junior at £24.99 is the better all-round helmet and the Ximo LE at £19.99 the value pick; for 51–53cm the Wilkinsons Junior at £7.50 does the job until we've more Alpina stock in. Replace after any impact, and don't buy second-hand.