Buying advice

Kids' Bike Size Guide: What Size Bike Does My Child Need?

Duncan McGregor·14 July 2026·2 min read

The short answer

Kids' bikes are sized by wheel diameter — 12", 14", 16", 20", 24" and 26" — not by frame size like adult bikes. The right wheel size depends on your child's height and inside-leg, not just their age. This chart matches every size to age, height and inside leg, then shows you how to measure properly.

Buying a kids' bike shouldn't need a spreadsheet. But because children of the same age can vary hugely in height, "what size for a [age]-year-old" only gets you halfway. This is the master guide — bookmark it. Below you'll find the full size chart, the one measurement that removes the guesswork, and a link straight to the detailed guide for your child's age.

The complete kids' bike size chart

Wheel size	Age (guide)	Height	Inside leg	Type
12"	1.5–3 yrs	85–100cm	30–42cm	Balance
14"	3–5 yrs	95–110cm	40–50cm	First pedal
16"	4–6 yrs	105–120cm	45–56cm	Pedal
20"	5–8 yrs	115–130cm	53–63cm	Geared
24"	7–11 yrs	125–145cm	60–72cm	Geared
26"	10–13 yrs	140cm+	70cm+	Geared

Where a child straddles two sizes, height and confidence decide it. Size down for a nervous beginner; up for a confident rider with room to grow.

How to measure your child's inside leg

Age charts are the starting point; inside leg is the decider. It tells you whether your child can plant their feet on the ground — the single biggest factor in whether a new rider feels brave or terrified.

Stand them against a wall, bare feet, heels back, in normal clothes.
Place a book between their legs, spine up, pushed gently to the crotch — mimicking a saddle.
Mark the top of the book on the wall, then measure straight down to the floor in centimetres.

Match that number to the bike's minimum saddle height. For a beginner, inside leg should equal or slightly exceed the lowest saddle height, so both feet reach flat. For a confident rider, a little tip-toe is fine and buys growing room.

Why kids' bikes use wheel size

Adult bikes are sized by frame (S/M/L). Children's bikes are sized by wheel diameter because it scales neatly with how tall a child is and how far they can reach the ground and the pedals. As a rule, each jump up — 12" to 14" to 16" and so on — represents roughly a year or two of growth. It's why kids typically move through three or four bikes before a full-size 26".