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Why size matters more than age!

Remember when you were buying baby clothes for your child, and the clothing was sized by age? Chances are you probably experienced some of those clothes not fitting your child during the age range listed. It’s the same concept for kids bikes. For example, your 12-month-old can be a lot taller or shorter than the average size, just like your 7 year old can be a different height than the average for each bike size. Not to mention, all bikes are not made equal. The same size bikes can actually have very different geometries depending on the bike manufacturer. You wouldn’t buy your kids clothes that didn’t fit, so why would you buy them a bike that isn’t the right size?

Size 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 first biking experience and lead to accidents. The kid's bike sizing guide below will give you an overview of the various kid's bike sizes, and show you how to choose the right size bike for your child based on rider experience, inseam, and height rather than age and wheel size.

What sizes do kids bikes come in?

Kids bikes come in these different wheel diameter sizes: 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 and heights. The most common sizes are: 12 inch, 16 inch, 20 inch, and 24 inch. As we will learn more later on in this post, you will understand why wheel size is NOT the best way to choose a bicycle for your child.

Kids Bike Wheel Sizes

Choosing the bike by 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.

Kids Bike Sizing Chart

Why doesn't this method always work well?

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. Notice how both bikes have 20 inch wheels but the bike in figure 1 has a smaller wheelbase and lower seat position. This bike has been specifically designed for a smaller kid.

Fig 1 - 20 inch small
Kids Bike 20 Inch Small
Fig 2 - 20 inch large
Kids Bike 20 Inch Large

Not to mention, the minimum seat height of two bikes with the same wheel size can vary up to 5 inches. There are more extreme examples if you begin to compare two bikes from different brands. Another issue with this method is trying to figure out which bike is going to last the longest and how long the bike is going to last.

Choosing the right size with inseam (the best way)

The most accurate way to find the right size bike for your child is to look at their inseam measurement along with the seat height of the bike.

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

  1. Have them stand up straight against a wall with their feet slightly apart and their shoes on.
  2. Measure their leg length and leg inseam. This measurement is the distance from the crotch of your child’s pants down to the floor.
  3. If you want to ensure your measurement is as accurate as possible, you can place a book (hardbound) between their legs and firmly against their crotch.
  4. The spine of the book should be the end closest to their crotch. Make sure the book is level and measure from the spine of the book to the floor!

Now that you have measured their inseam, you can begin narrowing down wheel size. Identify 1-2 wheel sizes their inseam aligns with (falls within the approximate inseam range) and choose the larger wheeled bike. There are two reasons why you should select the larger wheeled bike of the 2 you identified:

  • Larger wheels have more stability.
  • Larger wheels will save you money by leaving more room for growth before your child outgrows their bike.

Why riding experience makes a difference

Bike sizing is not a one size fits all approach for specific age groups. Two kids that are the same age can have different riding experience. Kids can also learn to ride on different types of bikes (balance bikes vs. bikes with training wheels), which can impact what pedal bike they are ready to ride.

Balance Bikes

12 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 1 - 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.

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 balance and prevents tip over accidents.

Pedal Bikes

A child's first pedal bike is one of the most exciting gifts of independence and freedom a kid will receive. With the growing popularity of balance bikes, children are now able to ride a pedal bike without training wheels as early as 3 years old! This has spawned a completely different way for kids bike brands to think about childrens bike design. A child's first pedal bike should fit differently than their second pedal bike (and beyond).

First pedal bike

On a child's first pedal bike, their heel should only be up off the ground 1 - 2 inches max. Timid riders should stick closer to 1 inch while athletic riders can be closer to 2 inches. This will put your child into a more efficient standover height and pedaling position while allowing them to touch the ground after braking.

First Pedal Bike

Second pedal bike

On a child's second pedal bike and beyond, they should be up on their tippy toes 2 - 3 inches. Timid riders should stick closer to 2 inches while athletic riders should be closer to 3 inches. Since children will be riding farther on their second pedal bike, they will want maximum leg extension for efficient pedaling.

Second Pedal Bike

How to match inseam and riding experience with seat height

Your main goal when buying a bike for your child should be to buy for current fit and growth. Although you want their bike to last as long as possible, you need to make sure the bike is the right size for them now, instead of being a size they will need to grow into. Buying too large of a bike may make your child struggle when riding, making it harder for them to build the proper riding skills and confidence. Bike riding is supposed to be a fun experience that your children enjoy and that keeps them active. Your kids will feel more comfortable and have more fun riding a bike that’s the right fit for them!

We recommend that your child’s seat height is set to be as close to the bike’s minimum seat height as possible when they first start riding the bike. As they grow, you can change the seat height accordingly.

Just as bike sizing is not a one fits all approach for specific age groups, it’s the same concept for inseam (which is why there are approximate ranges). For instance, A child may have a different torso size, which would change how they fit onto a bike. Although inseam is the most accurate way to find the right bike size it is not the only element you should consider. Inseam, seat height, riding experience, age, and height are all essential pieces of the bike sizing puzzle. That’s why we created a one of a kind RideSizer tool that incorporates all of those factors to find the perfect size bike for your child.

Choosing the right size Guardian bike with 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 16 inch, 20 inch, or 24 inch, is the best fit for your child. That is why we have launched a tool on our site called RideSizer - the world's first kids bike sizing tool that helps you choose the perfect bike for your child. Simply enter your child's height, inseam, riding experience, and birthday. 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. The tool also shows you exactly how your child will grow into the bike and educates you along the way. The tool is completely free and takes just a few second to get started. Give it a try here!

If you want to learn more about other factors you should consider before buying a new bike, read our kids bicycle buying guide article, or our article on bike safety for kids. We’ll touch on things such as why buying a bike online is better than buying from a bike shop and why a hand brake is safer than a coaster brake. We also share what the best kids’ helmets on the market and how to measure helmet size.


Find the perfect size bike