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

Getting the right size bike makes a huge difference to your child's confidence and safety. Too big and they can't control it; too small and they'll outgrow it in weeks. Here's how to get it right.

Size by wheel size

Kids' bikes are sized by wheel diameter, not frame size. Here's a general guide:

Height is more reliable than age. Children grow at different rates, so always measure your child's height and inside leg rather than going by age alone.

How to check the fit

• Feet on the ground: your child should be able to touch the ground with the balls of both feet when sitting on the saddle
• Standover height: standing over the top tube, there should be a few centimetres of clearance
• Reach: they should be able to reach the handlebars comfortably without stretching
• Brake levers: small hands need to reach the brake levers easily. Adjust lever reach if possible

Common mistakes

• Buying too big "to grow into": a bike that's too big is hard to control and dangerous. Better to buy the right size now
• Ignoring weight: cheap kids' bikes are often very heavy relative to the child. A lighter bike is easier to ride and more fun
• Stabilisers for too long: balance bikes teach balance faster than stabilisers. Consider removing them early
• Not adjusting the saddle: as your child grows, raise the saddle regularly to maintain proper leg extension

What to look for in a kids' bike

• Weight: lighter is better. A bike shouldn't weigh more than 40% of the child's weight
• Brakes: V-brakes or disc brakes with levers sized for small hands
• Gears: single speed for under-7s, gears for older children who ride hills
• Tyres: appropriate tread for where they'll ride (smooth for roads, knobbly for off-road)
• Quality brands: Frog, Islabikes, Forme, Squish, and Vitus make excellent lightweight kids' bikes

Second-hand bikes

Kids' bikes are often barely used before being outgrown, making second-hand a great option. But always check:

• Brakes work properly
• Wheels spin true (no wobble)
• Tyres aren't cracked or flat
• Chain isn't rusty or stiff
• Frame has no cracks or dents
• Headset and bottom bracket aren't loose

If in doubt, a basic service (£35) will catch any issues and make sure the bike is safe.

When to service a kids' bike

• Before the first ride — especially if bought second-hand or from a supermarket
• Every 6–12 months — depending on how much they ride
• Before the school year — if they cycle to school
• After a crash — check for bent wheels, misaligned brakes, or frame damage