How to choose the right size bike for your child

Buying your child the right size bike is the critical first step in getting them riding confidently. We tell you how

Kids grow fast, don’t they? It’s wonderful to see them getting bigger and bigger but when it comes to choose the right bike size for your child, the growing makes the process challenging.

Do buy your child a bike that’s a bit on the large size so that it’ll fit them in six months or so? Do you by based on age range or wheel size, which are often quoted by brands? It’s a tough one. But the answer is that neither is a good idea. We’ll tell you why and how to choose the right size bike for your child.

>> Save up to 31% with a magazine subscription. Enjoy the luxury of home delivery and never miss an issue <<

>>> Best kids’ bikes: tips for choosing a children’s bike

The right size bike will up their confidence

If you buy a bike that’s too large for your child, getting their feet on the ground will be difficult and the frame may not be low enough for them to stand over the bike and plant both feet on the ground. That’s more likely to make them feel nervous when riding and their cycling skills may be slower to develop – or they might be put off altogether. 

right size bike for child

The right size bike will make them confident to negotiate obstacles (Credit Islabikes)

The spatial relationship between the saddle, handlebars and pedals is likely to be wrong too. And components on children’s bikes are often sized to the child’s size, so dimensions like crank length and handlebar width may not be optimal and may be uncomfortable.

>>> Best cycle clothing for kids: a buyer’s guide 

Advice for choosing the right bike size

It’s a good idea to seek advice on sizing when buying a kid’s bike. Most bike shops will be able to give in-person advice on a child’s bike fit, and Halfords, for example, train all its store staff in fitting a bike for little riders. It has sizing advice on its site, too.

Children’s bike specialist Islabikes runs a call centre to help you with any queries and has a fitting studio and test track at its headquarters in Ludlow. Frog Bikes, which also specialises in kids’ bikes, sells through bike shops worldwide, so you can get fit advice in person. 



It is highly recommend using your child’s inside leg measurement to guide your bike choice. Islabikes’ size chart adds your child’s height as an approximate guide too, although Frog points out that most girls have longer legs for their height than boys and so may need their saddle set higher or even a bike that’s the next size up.

>>> Family cycling: how to enjoy a bike with  your kid

How to measure a child for a bike

First up, you want to measure their inside leg. Stand them upright against a wall, without shoes, then slide a book up between their legs until it sits firmly under their sitbones. Then measure the height of the top of the book from the floor to determine their inside leg measurement.

For their height, follow a similar process, but sit the book on your child’s head and measure the distance from the bottom of it to the floor.

These two measurements give you the basic information you need to look up which size bike to buy in brands’ sizing tables. If you want to keep the new bike a surprise, you can always pretend that you’re measuring them up to buy clothing over the internet or a new school uniform.

right size bike for child

A balance bike needs a low saddle height for your child to be able to scoot effectively (Credit Islabikes)

If you’re buying a balance bike, the minimum saddle height shouldn’t be greater than the child’s inside leg, so that they can push on the ground effectively. That’s also true of a first pedal bike too: your child should be able put their feet on the ground while in the saddle, for easy starting and stopping.

>>> Best balance bikes for toddlers

Once they’re older, riding more confidently and able to start and stop better, you can look at a bike where the saddle is between 2cm and 10cm longer than their inseam. This will make pedalling easier, as their legs will be less bent.

Why you shouldn’t use proxies 

Using a child’s age is not a good guide when choosing a bike size, as children grow at different rates. Wheel size is another typical way in which children’s bikes are sized, although that too isn’t a very good guide as it depends on the bike’s design.

To look at pedalling dynamics, Frog Bikes sponsored research using an adjustable rig to measure the most comfortable riding position for 142 kids between the ages of 7 and 16. It used this as the basis for its FrogFit phone app that you can use to find its recommended bikes and sizes. 

right size bike for child

FrogFit app recommends a bike and set-up based on your child’s measurements (Credit Frog Bikes)

Driven by the measurements of your child’s inside leg length and arm length, the app provides the recommended saddle height, reach to the bars and crank length, along with suggested Frog bikes, based on how confident a rider your child is. There’s a table on its website with its recommended bikes for different inside leg measurements too.

Make sure the bike can grow with them

It’s important to make sure that a bike has enough adjustment to set the minimum saddle height low enough for your child’s inside leg – and that there’s enough upward adjustment to fit them as they grow.

>>> Eight in one kids’ bike grows with your child

Although a quality children’s bike can be an expensive purchase, a bike from a quality brand that’s been well maintained and looked after will usually command a resale price that will help to recoup the initial investment. It’s likely that your child will have a happier riding experience too.