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Kids Bike Sizing Guide

Need help determining the right size bike for your kid? Check out our nifty sizing guide below! It should answer all of your questions!

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Use Guardian’s patented online sizing tool.

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Why is kids bike sizing important?

Bike sizing is the most important aspect to get right when deciding on a bike for your child. If the bike is too big or too small, it can ruin your child's biking experience and lead to accidents.

Why kids bike sizing is challenging.

When purchasing a kids bike, you should never choose a bike size based on an age range that is listed on a sizing chart. There are 2 main reasons for this:

  1. Kids the same age can be taller, shorter, and have different leg lengths than the average size kid.

  2. Kids bike sizing can vary greatly between different brands

    What, how can this be? This is because the same size bike can have very different geometries, especially when you find brands like Guardian Bikes that design bikes specifically for kids.

How we can help!

The kids' bike sizing guide below will give you an overview of the various kids bike sizes, and show you how to choose the right size bike for your child based on leg length and rider experience rather than the ineffective method of age and wheel size.

Bike Sizing

What sizes do kids bikes come in?

Kids bikes come in these different sizes which are based on the wheel size of the bike: 12 inch, 14 inch, 16 inch, 18 inch, 20 inch, 24 inch, and now even 26 inch. The wheel size is based on the diameter of the tire (see below) and as each tire size gets larger, so does the size of the bicycle frame. These different wheel and frame sizes help companies design bicycles that will fit kids of all ages. The most common sizes are: 12 inch, 14 inch, 16 inch, 20 inch, and 24 inch. You will learn later on why wheel size is NOT the best way to choose a bicycle for your child.

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How to Size

Bike Sizing by Height & Wheel Size: The Old Way

If you have ever purchased a bike before, you have probably seen a chart like the one below. These charts are designed for you to use your child's height to determine the correct wheel size. Sounds simple right? Then you finally get into the store, sit your child on a few bikes with the correct wheel size, only to realize that the bikes seem to fit differently.

Why doesn’t this method work?

The main problem is the size of the bike is not solely determined by the wheel size of the bike. The size of the frame and design of the geometry also matter. This is why the same company can have two 20 inches bikes that are designed to fit children of completely different heights. An example of this is illustrated below when comparing Guardian’s 20 inch small vs 20 inch large kids bike sizes.

Kids Bike 20 Inch Small

Figure 1: 20 Inch Small Bike

Kids Bike 20 Inch Large

Figure 2: 20 Inch Large Bike

Notice how both bikes have 20 inch wheels but the bike in figure 1 has a shorter wheelbase and lower seat position. This bike has been specifically designed for a smaller kid. There are more extreme examples if you begin to compare two bikes from different brands where the minimum seat height of two bikes with the same wheel size can vary up to 5 inches!

Another issue with this method is the difficulty in trying to figure out which bike is going to last the longest and how long the bike is going to last.

Bike Sizing by Leg Length: The Best Way

The most accurate way to find the right kids bike size for your child is to look at their bike leg length measurement and experience and compare it with the seat height of the bike. To make this easier, lets define each of these terms.

  1. Bike Leg Length = measured from the top of the crotch to where your child’s feet touch the ground (with shoes on!).

    Note - bike leg length is different than pant leg length.

  2. Rider Experience = some questions include: have they ridden a bike before? Did they start on a balance bike? Are they timid or confident?

  3. Seat height = this is the range of how low and how high the seat will go on a bike. For example, our Guardian 16 inch bike has a seat height range of 18.5 – 23.5 in

Measuring Bike Leg Length

Here is an easy step-by-step guide for measuring your child’s leg length:

  1. 1

    Have them stand up straight against a wall with their feet shoulder width apart and their shoes on.

  2. 2

    If you want to ensure your measurement is as accurate as possible, you can place a book (hardbound) between their legs and to the top of the crotch area.

  3. 3

    Measure from the ground to the top of the book (to their crotch) to get their bike leg length.

Rider Experience

Now that you have measured their leg length, the next step is to understand their riding experience.

If your child is under the age of 4 and has not ridden a balance bike or pedal bike before, we strongly recommend you take a look at starting them off on a balance bike. You can learn more about balance bikes at the bottom of this page.

This will be my child’s first pedal bike & did NOT use a balance bike Created with Lunacy Created with Lunacy

This will be my child’s first pedal bike & did use a balance bike Created with Lunacy Created with Lunacy

This will be my child’s second (+) pedal bike Created with Lunacy Created with Lunacy

Finding the Right Size

Now that you have measured their leg length and looked at their experience, the final step is to match that up against the seat height of a bike.

As parents, we like to purchase things (or items) for our kids that will last. When it comes to a kids bike, you will always want to get your kid on a bike towards the minimum seat height so that the bike has room to grow.

Minimum seat height = Inseam + heels off the ground (see above on experience)

I.E. a new rider with an leg length of 18 inches

  • Inseam = 18 inches
  • Heels off the ground = 0 inches
  • Minimum seat height = 18 inches

Now that you know their minimum seat height, you can start shopping around!

Want to make it easy on yourself? Use our RideSizer® tool below. Please note this only works for Guardian Kids Bikes.

The RideSizer®

Second Pedal Bike

Sizing by RideSizer®: The Future Way

Our goal at Guardian Bikes is to deliver you the safest children's bikes directly to your door. A big part of this is helping you choose whether our 14 inch, 16 inch, 20 inch small, 20 inch large or 24 inch, is the best fit for your child. That is why we have developed our patented RideSizer® tool - the world's first kids bike sizing tool that helps you choose the perfect size bike.

To use RideSizer®, grab your child's height or leg length measurements and enter some questions about their riding experience. For the most accurate sizing, we always recommend using your child's leg length measurement. RideSizer® will then show you exactly how your child fits on the recommended bike while also letting you know how long the bike will comfortably last.

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How Accurate is RideSizer®?

RideSizer® is over 98% accurate! For the past few years, we have been constantly improving the tool through continous learning and customer feedback. With tens of thousands of Guardian customers using the tool, RideSizer® has become increasingly more accurate over time. We are confident this will be the easiest way for you to size your kids’ new ride!

Balance vs Pedal Sizing

Balance Bikes

12 inch bikes and 14 inch bikes are typically equipped with pedals and training wheels, but over the last few years balance bikes, bikes without pedals, have started to gain more popularity. Instead of teaching kids to learn pedaling first and balance later, balance bikes take a different approach - teach kids balance first and pedaling later. This has been a gamechanger for teaching kids 2 - 4 years of age how to balance, and is the reason kids can now jump straight into their first pedal bike (14 inch +) without using training wheels.

If your child is under the age of 4 and hasn’t ridden a bike before, starting on a balance bike is the way to go. To learn more about balance bikes, please check out our Balance Bike Guide.

Balance Bike Fit

When sitting on the bike, kids this age should be able to put both feet flat on the ground and their body should be in an upright walking position. This helps children learn better balance and prevents tip over accidents.

Training Wheels Compatible

We recommend using the balance bike method when teaching your child to ride a bike, but understand all children learn differently.

Compatible training wheels can be purchased here for our 14", 16", and 20" Bikes.

🎁 Important!

Guaranteed Holiday Delivery ended at 6:30pm EST, on Friday, December 15th for all in stock bikes.

For all current in stock bikes, you will see a “May Arrive Before Christmas Badge”. This badge indicates we have inventory ready to ship out.

Please see transit times below. Note that these are estimated business days, and delays can be expected this time of year. We do not offer expedited shipping at this time.

Thank you, and happy holidays!

Bike being assembled

Assembly Steps

Step 1: Attach Handlebars

Step 2: Attach Pedals

Patented SureStop® Brake System

  • Easier to use – single lever braking

  • Safer to stop – prevents head over handlebar accidents

  • More control – stops faster by balancing front/rear braking automatically

Kid Friendly Gear Shifter

  • 7-speed twist shifter

  • Red visualizer to help with gear selection

  • Fun and easy way to learn