What Size Bike Does a Child Need? – Age is not size

No matter if your buying your kids bike as a way of transport or just for fun, kids and bikes go hand in hand.  When you’re looking at buying a bike for your kid, it’s really important to get the size right to make sure they are comfortable when riding it.  

If a bike is too small, they will feel cramped and perhaps embarrassed when riding it. If it’s too large, your kid might be afraid of losing control.  

You shouldn’t choose a bike based on age. Measure your kid’s height and inseam to find the correct size bike. 

Choosing the correct size of bike is a simple process but there are some key points to remember. With years of researching for our kids and speaking to many experts we’re able to give you some guidance to follow to ensure you can get the perfect fit for your kid. 

Age Is Not a Size 

The first point is not to choose a bike based on age. There are tall kids and small kids, so while it might provide some basic guidance, age alone is not enough to ensure that your child is going to be safe and comfortable on their new bike. 

Measure Height and Inseam 

Before we look at bikes you will firstly need to measure their height. If you can get them to stay still for long enough, whilst standing your kid next to a wall, rest a book on the top of their head and mark the point on the wall where it meets. Now measure this from the floor to their mark and that is their height. 

We then need to measure their inseam as this is another important part of choosing the right bike size. To do this you can place the book between your child’s legs and Nestle it snugly as if they were sat on a bike seat. Again, measure the point on the wall where the book meets it. Measure from the floor to this new mark and that is the length of their inseam. 

Armed with these two measurements you should now be able to get a much better idea of the bike size required. Most dedicated children’s bike manufacturers will list height and inseam measurements as a guide on their website or product listings.  

So, if your buying online or when you head into your local bike shop be sure to check these details. 

To help a little we’ve prepared our kids bike size charts based on height and inseam. 

Kids Height
(Feet & Inches)
Kids Height
2’9″-3’1″85-90 cm10 inches
3′.1″-3′.3″90-100 cm12 inches
3′.3″-3′.7″100-110 cm14 inches
3′.7″-3′.8″110-115 cm16 inches
3′.8″-4′.0″115-120 cm18 inches
4′.0″-4′.5″120-135 cm20 inches
4′.5″-4′.9″135-145 cm24 inches
5′.0″ or above145 cm or above26 inches
Kids Inseam
Kids Inseam
12″-14″ 30-35 cm10 inches
14″-17″35-42 cm12 inches
16″-20″40-50 cm14 inches
18″-22″45-55 cm16 inches
20″-24″50-60 cm18 inches
22″-25″55-63 cm20 inches
24″-28″60-72 cm24 inches
28″ or above72 cm or above26 inches

What is the Right Size? 

Now that you’ve bought the bike how do you know that is set up at the right size? The first thing that we need to look at is when they are sat in the saddle, they should have one foot on the floor and one foot on the pedal. At the bottom of its stroke, their knee should be slightly bent. Exactly the same as it would be for you if you were sat on an adult bike. 

Also, when they’re sat on the seat with both feet on the floor, make sure that balls of both feet can reach the floor for stability. Make sure that seat is not too low because if it is, pedalling will be extra hard for them. It will also make balancing a bit harder too, as their knees cannot move from side to side. 

A balance bike is slightly different to this though. The saddle should be set that your child can get their foot flat on the floor and still have a slight bend in the knee. 

Brakes, Gears and Pedals 

Whilst ensuring that we are choosing the correct frame and wheel size for your child is probably the most important part, other points to consider so that the bike can be truly comfortable and fun to ride for your child are things like brakes. You will need to make sure that their hands are able to easily reach them

You can also look at the diameters of the handlebars. If they are slightly smaller, it’s going to make them more confident on the bike. Also, with the brakes, make sure they can easily pull the levers on. 

Look also at the cranks and the pedals because they need to be in proportion with the rest of the bike. Shorter cranks particularly mean that the saddle can be set in the right height but when the pedal comes up the knee and the hip aren’t going to have to bend too far, so your kid will be more comfortable. 

It also means the whole bike itself can be a little bit lower and still have plenty of clearance when going around corners. 

Younger Children’s Sitting Position 

Something that we weren’t aware of, until speaking to experts is that younger kids need to sit more upright on their bikes than older kids. This is because their internal organs are proportionally much much larger. 

There’s still plenty of time for them to get aerodynamic later. Usually between the age’s of about five and ten. At the moment it will be less comfortable for them to be hunched over. It’s also easier for your kid to learn to ride a bike when they are sat upright.  

Don’t Rush Them Onto Bigger Bikes

A common mistake when getting a new bike for your child is to choose one size too big, so they’ve got some time to grow into it. This is something i know lots of people have been guilty of doing in the past.  

However, we need to steer clear this temptation because a bigger bike is far harder for them to handle and much less enjoyable for them to ride. It could also potentially dent their confidence and it should go without saying but it’s just not safe

Bigger wheels on the bike could make the bike easier to handle. It would be more stable and better help your kid to handle bumps. In my opinion if you have a choice between a 16” wheel bike and a 20” wheel bike and your child is equally comfortable on either then you should always go for the larger wheels. 


Choosing the right size bike for your child is ultimately just about making sure that they are comfortable.  

  • Don’t chose a bike size based on their age  
  • Remember that younger children need to be more upright 
  • Every part of the bike needs to be in proportion 
  • Make sure your kid is always wearing a helmet. 

If you need any help with choosing the right size helmet, we’ve previously written an article where we discus how to measure your kids head, things to consider and top brands. You can view it here

The Warburton Family

Everything we write is tried and tested. We research everything before putting it out to the world. Thanks for reading :-)

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