Kids bikes are sized by wheel diameter, not frame size — and inseam matters more than age. A 5-year-old around 43–47 inches tall with a 17–19 inch inseam is on a 16-inch wheel; a 7-year-old at 47–53 inches is on a 20-inch. Measure the inseam before you buy anything.
Inseam decides whether your child can stop safely. On a first pedal bike they should be able to put both feet flat on the ground while seated. On a bike they can already ride confidently, the balls of both feet touching is enough.
Kids bike size chart by age, height and inseam
| Age | Height | Metric | Inseam | Metric | Wheel | Metric | Type |
|---|---|---|---|---|---|---|---|
| 2–5 yrs | 33½–43⁵⁄₁₆” | 85–110 cm | 11½–13″ | 29–33 cm | 10″ | 25.4 cm | Balance bike |
| 2–4 yrs | 33½–39⅜” | 85–100 cm | 13½–16″ | 34–41 cm | 12″ | 31 cm | First pedal bike |
| 3–5 yrs | 37⅜–43⁵⁄₁₆” | 95–110 cm | 15–18″ | 38–46 cm | 14″ | 36 cm | Pedal bike |
| 5–7 yrs | 43⁵⁄₁₆–47¼” | 110–120 cm | 17–19″ | 44–48 cm | 16″ | 40 cm | Pedal bike |
| 6–8 yrs | 45¼–51³⁄₁₆” | 115–130 cm | 18–20″ | 48–56 cm | 18″ | 46 cm | Pedal bike |
| 7–9 yrs | 47¼–53⅛” | 120–135 cm | 19–22″ | 48–56 cm | 20″ | 51 cm | Kids MTB / BMX |
| 9–11 yrs | 53⅛–57¹⁄₁₆” | 135–145 cm | 22–25″ | 56–64 cm | 24″ | 61 cm | Kids MTB |
| 11–15+ yrs | 57¹⁄₁₆” up | 145 cm up | 24–28″ | 61–71 cm | 26″ | 66 cm | Small adult frame |
Where the age bands overlap — and they overlap a lot — go by inseam. A tall five-year-old belongs on a 16-inch wheel even though the chart also lists 16-inch for six-to-eight-year-olds.
A current 16-inch pedal bike option:
How to measure your child’s inseam for a bike
Shoes on, a book, and a wall. This is the measurement bike shops use and it takes a minute.
- Stand your child with their back against a wall, feet about shoulder-width apart, wearing the shoes they will ride in.
- Put a hardback book between their legs, spine up, and raise it firmly until it sits like a saddle — snug, not painful.
- Mark the wall at the top of the book’s spine.
- Measure from that mark straight down to the floor. That is the inseam.
Can they ride a bike they have to grow into?
Not safely. A bike that is too big is the main reason children lose confidence early — they cannot get a foot down at a stop, so every junction becomes frightening. Buy the size that fits now; kids bikes hold their resale value well precisely because everyone has to keep moving up.
Balance bike or pedal bike first?
A balance bike from around two years old teaches steering and weight-shifting without the complication of pedals, and children who start on one usually skip stabilisers entirely. If your child is already four or five and confident on their feet, going straight to a 14 or 16-inch pedal bike is fine.
A current balance bike option:
Helmet fit matters more than bike fit
Whatever bike you choose, the helmet should sit level, two finger-widths above the eyebrows, with the straps forming a V under each ear and no more than one finger between strap and chin. Look for a helmet certified to ASTM F1447 or CPSC. A chart gets a bike close; a helmet needs checking on the child’s actual head.
A current CPSC-certified kids bike helmet:
Sources and verification
Wheel-size bands above are the standard used across kids bike retail. Helmet certification references the ASTM F1447 standard and the US CPSC bicycle helmet requirement. Manufacturers vary — particularly in standover height and reach — so check the specific model’s own geometry chart, and where you can, have your child sit on the bike before buying.
Last verified: 5 August 2026. Spotted a number that looks wrong? Tell us — corrections get the chart re-checked and re-dated.
More charts: every kids size chart in one place.
