Toddler helmet size chart

That table is the answer. Measure your toddler's head circumference with a soft tape about an inch above the eyebrows, find the band, and buy a helmet whose published centimeter range contains that number. Everything below covers how to take the measurement on a child who will not sit still, and what to check beyond the size.

How to measure a toddler's head

What each toddler-size band actually covers

The bands in the table above are built from the published ranges of four brands, and the overlap is substantial. A 49 cm head falls inside the Giro Scamp XS (45 to 49 cm), the Giro Scamp S (49 to 53 cm), the Giro Tremor Universal Child (47 to 54 cm) and the Bell Sidetrack II Child (47 to 54 cm). When a measurement lands at the edge of two sizes, take the smaller one — a helmet can be padded down a little but it cannot be made smaller.

The certification detail that matters under five

All bicycle helmets sold in the United States must meet the CPSC standard at 16 CFR 1203, but brands state different minimum ages for different models in a range. The Giro Scamp is the clearest example: Giro certifies the XS for age one and older, and the S for age five and older. Buying the larger shell for a two-year-old because it will last longer takes you outside what the manufacturer certified.

For a child under about three, look for extended coverage at the back of the head. Toddlers fall backwards far more often than older children, and a toddler-specific shell drops lower at the rear for exactly that reason.

A size that fits is not the same as a helmet that fits

Circumference gets you the right shell. Three more checks get you a helmet that protects:

Two fingers above the eyebrows. The front rim should sit about two of your child's finger widths above the brow, not tipped back on the crown.

Straps form a V under the ear. The side straps should meet just below and slightly forward of the earlobe.

One finger under the chin strap. Done up, you should just be able to slide one finger underneath. Ask them to open their mouth wide — the helmet should pull down slightly.

The full method, with what each check is actually testing for, is on how to fit a kids bike helmet.

When to move up a size

Not on a birthday. Move up when the dial adjuster is at its loosest setting and the helmet still feels tight, or when the pads have been removed and it still will not sit level. A toddler's head grows quickly in the first two years and then slows sharply, so a helmet bought at two often fits until four or five.

Replace it rather than resize it after any impact, even one that leaves no visible mark — the foam crushes internally and does not recover. The timeline for routine replacement is on when to replace a kids helmet, and the toddler helmets we would buy are on best toddler bike helmets.

Why toddler helmets run in such narrow bands

A toddler's head is close to its adult circumference long before the rest of them catches up — which is why the bands are narrow and why guessing is risky. Between one and three the circumference changes by only a few centimeters, so a helmet bought correctly at eighteen months often still fits at three. That also means a helmet bought two sizes large will still be two sizes large a year later.

The practical consequence: do not buy up. The usual argument for sizing up — that they will grow into it — barely applies here, and the cost of a loose helmet is immediate.

Weight and coverage, the two toddler-specific checks

Weight. A toddler's neck is proportionally weak, and a heavy helmet encourages the head-down slump that makes them look where they are not going. Published weights are rare at this size, but the in-mold construction used by the Giro Scamp and Bell Sidetrack II is lighter than a hard ABS skate shell for the same coverage.

Rear coverage. Toddlers fall backwards far more than older children do, because they are still learning to catch themselves forwards. A toddler-specific shell drops lower at the back of the skull for exactly that reason. Hold the helmet beside a youth helmet of the same brand and the difference in the rear profile is visible.

A flat rear profile is also worth checking if the child will ever sit in a bike seat or a trailer, because a helmet with a pronounced tail pushes the head forwards against a seat back.

Converting between centimeters and inches

American listings often quote inches and the manufacturer's own chart quotes centimeters, which is where sizing mistakes creep in. Divide centimeters by 2.54 to get inches, or multiply inches by 2.54 to go the other way. The table above gives both for each band so you do not have to.

If you only have a string and a ruler marked in inches, measure in inches and convert once rather than estimating twice. A half-inch error is more than a centimeter, which is enough to put you in the wrong band at the edges.