The Definitive Guide to Kids Bike Sizes (Don’t Buy the Wrong Bike)

Children on bikes

Kids love riding bikes.

Remember the sheer thrill of riding your first bike? More likely than not, it is one of the presents you will never forget.

As a bonus, it gets kids fit, gets them outside, offers them some independence, and most all of riding is fun. The great news is that kids can start properly riding bikes from about 3 years of age.

But kids don’t stay the same size for long. Everyone knows this. It’s a fact of life. That’s why choosing the right bike for your kid, can initially seem quite confusing, but is also crucial to their being able to ride their bike safely and with confidence.

When selecting a bike for a younger person, the most important things to ensure is that the child looks and feels comfortable on the bike, and that they think the bike is cool: Don’t get your kid a bike that they blatantly don’t like the look of, and hope they’ll change their minds once you get them back home.

They might, and they might not.

The last thing you want to do is scar your child emotionally for life by buying them a Destructor 4000 Extreme when what they wanted was the Princess bike with a basket and sparkles. Been there, done that.

Kids have never had so much choice of quality when it comes to bikes. From teenagers to toddlers, there’s a bike for your child.

But if you buy a bike that is too small your child may feel silly sitting on it, and also feel cramped. Conversely, buying a bike that is too large will be unwieldy, difficult to control, and undermine their fledgling confidence on the pedals.

Be under no illusion, the whole thing is a minefield, but a minefield you can cross.

Child fixing bike

Buying your kid a bike isn’t as simple as it was in the old days

At least not as simple as it was for me. When it came to my parents choosing the perfect bike for me it came down to which one of my brothers’ old bikes I wanted out of the garage. Having chosen, my father would lift the bike down off the peg, made sure it wouldn’t fall apart, and then said I had to be home before dark.

As adults, the proper way we choose our bikes is by reference to the frame size. If we can stand over the bike with our feet planted on either side of the upper tube, then we can say with some certainty the bike fits. This is not how you choose the right size bike for children.

Fear not though, because fortunately there are guides and guidelines for helping you choose a bike that is perfect for your child’s age and size.

Bike shop

What size bike does your child need?

When choosing a grown up bike, we use the size of the frame as our reference point. But when it comes to kids bikes we actually use the diameter of the wheel as the reference point. That’s because kids’ wheel sizes that determines the proportions for the rest of the bike. Kids’ wheel sizes are generally available in 12, 16, 20, and 24 inches. At 26 inches you’re into the standard sized adult mountain bike wheel size.

Roughly speaking, 12 inch wheels are designed for kids starting off biking and who on average are aged between 3-5 years of age, and by the time your child is 14 years old, you will mostly be looking at 24 inch wheel.

So how do you discover what size bike is perfect for your child?

The general rule of thumb is to use a sizing chart. Sizing charts are available from all good bike websites and stores. There are slight variations in some of them, especially when moving to adult sizing charts, but for children they do remain fairly consistent. Below is a good example of one that can be followed:


Wheel Size Age Height
12″ 2-3 2’10”-3’4″ 85-100 cm
14″ 3-4 3’1″-3’7″ 95-110 cm
16″ 4-5 3’7″-4’0″ 110-120 cm
20″ 5-8 4’0″-4’5″ 120-135 cm
24″ 8-11 4’5″-4’9″ 135-145 cm
26″ 11+ 4’9″+ 145+ cm

Another useful form of chart for determining the right size of bike, and some might say more accurate, is the inside leg length approach.

Wheel Size Age Inseam Inseam
12″ 2-3 14-17′ 35-42 cm
14″ 3-4 16-20′ 40-50 cm
16″ 4-5 18-22′ 45-55 cm
20″ 5-8 22-25′ 55-63 cm
24″ 8-11 24-28′ 60-72 cm
26″ 11+ 26+’ 70+ cm

Young boy biking

Height charts are not the definitive factor when choosing a kid’s bike

Height charts are not the be all and end all when it comes to picking your kid’s bike. Think of them more as a starting point to help give you an idea of what you after.

If the sales guy in the local bike store insists on only using a height chart when you visit, then turn round and walk away.

By far the most important thing to do is to get a test ride and observe how well your child is able to ride easily and in a controlled manner. There are other factors at work other than overall height. You must take into account the proportions of your kid’s body and personal riding disposition.

Girl on bike

The importance of getting the right fit

Despite what some might say, choosing the right size bike in not a precision science. Guides and charts are useful but nowhere near as useful as watching your kid actually test out a bike. The bike should fit the child, not the other way round.

Safety is paramount. This is why you should never buy a bike that is too large for your child in the hope that ‘they will grow into it.’ Your child should be able to straddle the middle of the bike with their feet flat on the ground on either side of the bike with a good inch or two of clearance. They should not have to lean the bike one way or the other to get a foot flat down.

You have to consider what happens if they suddenly need to hop off the bike quickly. This is especially true if your kid is a boy and you think you might like grandchildren one day. The bike should only have a slight lean when your kid puts their bottom onto the seat, puts one foot on a pedal and then scoots away.

When your child is riding away, they be seated in a mostly upright position, and their knees and legs should not be bouncing of the handlebars. On the other hand, their legs also should not be completely stretched out at the lowest vertical position of the pedals either. There should always be a slight bend in the leg.

Children should also be able to turn the handlebars in a sweeping motion to their full extent without being overstretched. Younger children tend to use the turning arc of the handlebars to steer more than older children and adults, who will also use balance to negotiate turns and corners.

Bicycle mechanic

Expert advice is invaluable

Never ever underestimate the power of good advice given by an expert. 5 minutes with an experienced and reputable bike expert can you save you hours spent scouting the internet for the answer.

As can often be the case with Google, you can find yourself with a 100 new questions and more confused than when you started.

Family biking together

Why do some kids bikes seem to weigh as much my own bike?

Fortunately, that’s no longer necessarily the case. The fact is that it used to be that kids’ bikes would be the only thing a Twister in Missouri would leave behind. The cheap ones still are.

But more commonly these days, most bike manufacturers now offer decent value lightweight bikes for your kid. This is an important fact to be aware of as proportionally speaking, kids’ bikes are harder to pedal than adult bikes anyway due to the smaller wheel base. So if you can, do try to buy as light as you can.

Father and son biking

Start them young, keep the keen!

  • Balance bikes, 2-5 years old: The younger you start your kid riding, the more confident they will be getting on a bike in later life. A great place for a young kid to begin their cycling odyssey is with a balance bike.

    Balance bikes are exactly what they say they are. They have no pedals, and tend to only have a have brake. They are brilliant for letting your kid develop their sense of inertia and balance and learning how to steer, and as they have no means of propulsion other than how fast they can push off the ground, they are relatively safe to use indoors, and are of course, a generally safe way to learn overall.

  • Basic Small Wheelers, 3-6 years old: These are your classic first ‘proper’ bike models. Typically they come with 12, 14, and 16 inch wheels at the outside. Some bikes in this range do come with simple gear sets and basic front fork suspension, but my advice to you is not to bother. They will more likely than not be cheap and add more weight than you child needs.

    The most important factor here is the fit, as discussed above. Make sure the kids’ feet can easily touch the ground, their hands can reach the brakes on the handlebars. This is where, in my experience, riders are born or broken. Unlike balance bikes, their feet will be on the pedals, not trailing along the ground for extra stability.

    They will also be going faster. What this means is they are now at the stage where they are more likely to have the occasional accident. Kids can deal with the occasional accident, but not if it becomes a familiar occurrence. So make sure you buy the right size.

  • The next level: 20 inchers, 6-9 years old: This is unfortunately where are most likely to come face to face with your first proper set of gears, and proper suspension. Geared versions of these bikes will come with between 5 and 10 gears, with hill climbing firmly in mind as opposed to speed.

    While not a necessity, it is handy for getting children used to how gears work. As a youngster, I rode BMXs up to the age of 16. As a result, despite owning a fully-fledged mountain bike, road bike, and folding bike, I still don’t fully trust or understand gears.

    Don’t bother with the bikes in this category that come with front fork suspension either. Yes they look cool, especially if you’re a kid, but the chances are the forks will be cheap, heavy and not actually be effective. The truth is that fully rigid bikes at this level will not only be lighter, but also be higher quality.

    If your kid is insisting on forks, then either buy the lightest frame possible, or upgrade to some 3rd party suspension forks. It will be money well spent.

  • Growing up too fast: 24 inches and bigger, 9-14 years old: Read the above bits about suspension and gears again, and just add it in here. The same is true for these semi adult bikes, as it is for 20 inchers. This is where you can start to find all the bells and whistles most normally associated with full adult bikes. Not only might you start to find bikes with up to 36 gears, but also things like triple chain sets.

    In my opinion these additions still just add extra weight and are more complicated, and are not worth the extra money at this level. If you can, let your kid be a kid just that little bit longer. If they insist on gears, then try to limit them to single or low digit gearing.

Children bike race

Mountain bike or Road bike?

Up to 24 inch wheel sizes, almost all kids’ bikes come in the mountain bike style with the wide, grippy tires and horizontal handlebars.

24 inch wheels start to give you the option to buy slick tired bikes with the racing bike drop handlebars. Really, it all comes down to what your kid wants to ride.

My best advice here is to stick with the mountain bike style until they fully progress to a grown up bike. That said, if all they do is ride on roads, and never go off road, then perhaps a road bike is the way forward. Whatever you do, make sure they try them out first. Your kid may either love the road bike or hate it, so it’s best to try it out first.

BMX kid

What about a BMX?

Why not give your kid something they might want to ride for years and years? As I have already stated, I rode mine solely all the way up the age of 16 before I finally managed to break it. That was a solid 8 years of almost constant daily use!

BMX style bikes have an awful lot going for them. They are tough, single geared, extremely durable, and their resale value is quite high.

The best thing about BMX style bikes though is their inherent ability to go anywhere and deal with any biking situation life can throw at them. By their nature they are small wheeled bikes, which means, as I’ve already stated, kids can start using them at a very young age, and many kids’ versions will come with a 12 inch wheel.

Even when moving to a fully sized 20 inch wheel BMX base, the bike is exactly the same, just slightly bigger. One of the big plusses of a BMX is that for the same money as a kids’ mountain bike, you’ll probably end up with a lighter and better bike overall.

Kid biking with parents

Final thoughts

Get the right size at the right time. Make sure the bike fits. Use the size guides, but remember they are only guides. Make sure they look comfortable on the bike. Make sure your kid wants the bike you’re buying. Buy the best you can afford, but don’t be stupid with your cash either.

Don’t bother with all the bells, whistles and heavy fancy gadgets bolted on to appeal to easily influenced minds. Do get expert advice, but do some research first so you can at least understand what the expert is talking about.

Really final thoughts

Be responsible and teach your kid how to be safe when they ride, wherever they ride.


Kids bike helmet


  1. This was SUCH a helpful article. After read your article, I can get the right size for my 3 year old little boy. But I think if your child is less than 5, wearing the helmet will affect their head, I mean is cervical spine so be careful. Thanks so much for this article.

  2. I think they are too young to wear the helmet, because their bone still longer soft.

  3. My son is almost 4 but very tall for his age. Buying his first bike for Christmas so I can’t exactly let him try them all out. On both the height and inseam, my son is on the lowest range number for the 16′. Just worried it will be too big. Any advice?

  4. Great information! Very helpful. I had to chuckle at the last section where in bold it reiterates that kid’s should ALWAYS wear helmets… yet one of the first pics of the family biking along a leaf covered trail- not one of them’s wearing a helmet.

    Finger pointing aside, since those pics were clearly promotional, I’m so glad to have this info as our kids are also getting bikes for christmas and won’t be able to get on them until Christmas day.

  5. Be careful when adding aftermarket suspension forks to a bike that didn’t come with them from the factory. Sometimes the head tube angle can become dangerously steep when the suspension is at full compression. This, in very extreme situations can cause a head tube to become compromised, leaving the rider in a bad spot!

  6. Very clearly communicated article, thanks for taking the time. So it’s Christmas eve and I just finshed assembling my 8 yr old daughters first full size bike. Its a 20″ Mongoose Byte Girls’ Bike and with an inseam of 24″ im beginning to think maybe i needed to get a bigger bike?
    My considerations though, are that:
    1. She’s still not learned to actually ride a bike without training wheels, so getting her something she could control and felt comfortable riding was top priority.

    2. Ideally i wanted to get a lightweight bike as she is pretty wiry (all legs), basically for the same reason as mentioned above. But my budget was really tight so here we are,

    I guess what im asking most is, would it be better to just return this bike for a more appropriate size since every chart i’ve seen says she’s borderline too long for this one, or just stick with the smaller bike as it might appear less intimidating, lighter and easier to handle, or go ahead and get the 24″ inch since apparently it’s the most appropriate size for her going forward? I’m torn

    • Sounds like the 20″ might soon be too small for your daughter, so maybe it would be a good idea to exchange it for a 24″ so she can keep using the bike for as long as possible (as long as she can ride a 24″ safely, i.e. that a 24″ isn’t too big for her).

  7. Hello I want to buy a bicycle for my sister. She’s 8 years old. I don’t know which bicycles that I should to buy for her. please recommend me to buy it thanks

  8. Hi, Please help!

    My almost 5 years old son been avoiding riding bicycle until now, he have a new bike in the garage (been there over a year! unattached) now he have decided to have a go…
    His 12″ bike seams to small and he really have a problem when pedalling. Due to salesman advice the bike is right size for him , he have a good balance skills but if I insist on getting another bike I should get 14″ one.
    My question is is it necessary to go size by size on bikes or can we go straight to size 16″ BMX bike? My son is 109cm tall.

    Thank you.

  9. Thank you Mads Phikamphon for sharing this article.

    My daughter won’t buy wrong bike anymore. Because I had followed your introduction :)

  10. Hi, looking for sizing for a cruiser for my 16 year old daughter. She’s a bit tiny for her older sisters 26 inch Raleigh. She’s 4 ft 11 inches, 98 pounds with a 27 inch inseam. Wears only a size 3 shoe. Looks like they make the cruisers in a 20inch, 24 inch and the 26 inch. Which would be best for her? Her sisters Raleigh 26 inch has the large balloon tires so I’m not sure if that is making a difference in her being comfortable on it? Thanks for any help.

  11. Slim Shapely says:

    Those are the whitest human beings I’ve ever seen.

  12. hi im 12 and i am a boy who is really into road racing i am about 5 feet tall and my mom and i need help finding a good bike for me to use please answer back

    thank you very much in advance

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