The Frog kids bike sizing guide


The Frog kids bike sizing guide

How do you find the right bike size for your child?

We all remember receiving hand-me-down bikes that were usually too big and being told: “don’t worry, you’ll grow into it.” This phrase is of little solace when your heart is in your mouth because you can barely see the floor let alone put your feet on it!

Here at Frog, we take sizing a child very seriously! This is one of the most important factors for cycling success and enjoyment.

Children’s bikes were historically sized using the wheel size rather than the frame size (the convention for adult bikes). However, every manufacturer’s frames are different, standover height and saddle height can vary wildly on bikes which have the same size wheels and claim to be the same size.

You will often see Wheel Size and Age referenced as the best methods to pick a child’s bike but this is not correct, the main measurement you'll need is your child’s inseam measurement. Once you have this then you can go on to look at your child’s arm length and wheel size to ensure the bike will allow for growth.


Children are unique and come in all shapes and sizes, growing at different times. You can have extremes of height in all age categories so trying to fit everyone neatly into an ‘age 4’ box simply doesn’t work!


Height is more useful than age but still not perfect. After all, between boys and girls, there may be a difference between leg length and torso length. Most girls tend to have longer legs and shorter torsos compared to their male counterparts and this will mean they may need a higher saddle position and maybe even a bigger bike than a boy of the same height.

WHEEL SIZE - Worth considering

Whilst many companies use a similar wheel diameter on their frame sizes, some manufacturers have chosen to put larger wheels on smaller frames in an attempt to increase stability. For this reason alone, using kids' bike wheel sizes to choose a bike isn’t always possible. Wheel size can be taken into account at a later stage which we will discuss in a little bit!


This is the most important measurement and the best way to find the right bike size for kids. This way you can find out if when they are sat on the bike they will be able to put their feet on the floor (when the saddle is at its lowest). In addition to this, you will be able to get an idea of how long the bike will be the right size for them - by looking at the maximum saddle height.

How to measure a child's inseam

  1. Stand your child, in their socks (no shoes) against a wall
  2. Place a small book between their legs (with the spine upwards), as high as is comfortable
  3. Ask the child to move away and measure from the spine of the book to the floor

It’s that simple! Once you are armed with their inseam measurement you can then go on to consider what wheel size they will probably need. Generally speaking, kids who are just learning to ride should have a bike with 10” or 12” wheels, this will of course change if they are learning to ride at an older age.

Often when kids get to the point they need 26” wheels they are forced into the adult category, where bikes weigh twice as much and will be a lot harder to handle. Frog offer Hybrid , Road , Track , MTB and City bikes in a 26” wheel size to ensure that a taller child isn’t penalized and forced to ride an adult bike before they’re ready.

Our Frog Fit app offers size suggestions for both confident and tentative riders when you input their inseam measurement. This is based on the idea that a confident rider won’t mind if just their tiptoes are on the floor when sat on the saddle, compared to a more cautious rider, who will want to feel their feet flat on the ground when seated on the bike.

What else should I consider?

Standover Height
This is the distance from the ground to the top tube of the bike frame. We recommend that your child can stand comfortably over the top tube of their bike (when they are standing with one leg on either side of the bike). You need to ensure your child’s inseam is at least as tall as the standover height measurement. It’s best to have a little bit of extra room here too.

Minimum Seat Post/Saddle Height
Frog Bikes have long seat posts (and you can purchase an additional handlebar riser ) to ensure the bike can grow with your child and remain a good fit for as long as possible. It is also helpful to know the minimum seat post height to ensure your child will be able to touch the floor.

The minimum saddle height should be looked at in different ways depending on the bike.

For a Balance bike, the minimum saddle height should be no higher than your child’s inseam measurement. Ideally, the seat should be set at anywhere from 2 - 4 cm below your child’s inseam measurement. For example, if they have a 32 cm inseam you should set the saddle height around 28-30 cm (distance from the floor to the top of the saddle).

Your child needs to be able to get his or her feet firmly on the ground to scoot and balance, if the saddle is too high then they will not be able to reach the floor to propel themselves, forwards. This set-up also allows your child to place their feet flat on the ground with a slightly bent knee. The bend in their knee will allow them to run on the bike as they become more confident.

For a First Pedal bike, you should again be looking at a bike that has a minimum saddle height the same as your child’s inseam measurement. They should be able to touch the ground when seated on the bike allowing them to stop and start without toppling off.

If they started with a Balance bike and are already very confident this measurement can be 2-3cm higher than their inseam. This simply means they will be on their tiptoes rather than flat feet.

As they become more confident the saddle can be raised a little higher allowing for better leg extension when pedalling, which will increase their pedalling efficiency.

For their second pedal bike, it is absolutely fine to only be able to touch the ground with their tiptoes. A confident pedaler may even have the saddle position 5-10 cm higher than their inseam measurement.

Why choose a Frog bike?
Frog Bikes are designed purely for children. Along with our ethos to build bikes with the child at the centre of everything (from the components to the colours), our frame geometry has been specifically designed to give a child a comfortable and in-control riding experience.

Our research was led by Dr Tom Korff, now the Head of Research and Design at Frog Bikes, this formed the basis of a PhD research paper that can be read in full Here (for any bike geeks out there)! During his study, an adjustable bicycle fitting rig for children was built, to find the most comfortable riding position for 142 children aged from 7 to 16. In addition to this, a number of other body measurements were recorded.

Using the data from Dr Tom Korff’s study we went on to create the FrogFit App. Originally used by our local bike stores, we have now made this available to everyone. It doesn’t matter if you are buying in your local bike shop or second hand from a neighbour you can now use our app to ensure you have found the perfect Frog bike for your child.

When you consider all the hard work we put into making sure our bikes are tailor-made for little riders it would be a huge shame to fall at the last hurdle and select the wrong size bike for your child. So download the FrogFit app today and you can ensure smiles for miles on your next family bike ride!

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