Ultimate Guide To Kids Bike Sizes (And Bike Size Chart!)

Author: Kristen Bonkoski


The number one email question I get in my inbox: “What size bike does my kid need?”  Let’s be honest, it’s confusing!

For starters, kids bikes are sized differently than adult bikes (by wheel size rather than frame size).  Also, even when we’re talking about a bike with certain size wheels, the standover height and seatpost heights amongst manufacturers can vary drastically.

kids mtb shorts

Finally, while a bike might be advertised for a 5-year-old, some 5 years olds are tiny while others are huge.  There’s no way those two kids will be best served by the same bike.

That said, you can figure out the right size bike without trial-and-error, or pulling your hair out.  We’ve helped hundreds of parents figure out which size kids bike to get.  Here are 3 tips to help you get the right size bike the first time.

woom 4 geometry

1) Know What Wheel Size Your Child Needs

Kids bikes are “sized” by the diameter of their wheels.  The tiniest pedal bikes start with 12-inch wheels while bigger bikes go all the way up to 24-inch wheels.   When your kiddo is ready for 26-inch, they are generally ready for an adult size ride, although some bike manufacturers make smaller “youth” size 26″ bikes.

Balance bikes, on the other hand, start with wheels as small as 10″ although most balance bikes have 12″ or 14″ wheels.  

The best way to start narrowing down which size bike your child needs is to determine which size wheels they PROBABLY need.  I say probably because we’re basing it on an age range for kids of average height. 

If your child is tiny or super tall, they may need a smaller OR bigger bike than the general range we suggest here.  Don’t let that stress you out–this is just a starting point, so get a basic idea of what size wheels your kid PROBABLY needs.

Kids Bike Size Chart

Remember, this is just a starting point.  Use this chart to get a general idea of which size bike your child needs, but don’t skip the steps below!!!!

Wheel size Age Height Inseam
12” 2-3 2’10”-3’4” 14-17” 35-42 cm
14” 3-4 3’1”-3’7” 16-20” 40-50 cm
16” 4-5 3’7”-4’0” 18-22” 45-55 cm
18” 5-6 3’9”-4’3” 20-24” 50-60 cm
20” 5-8 4’0”-4’5” 22-25” 55-63 cm
24” 7-11 4’5”-4’9” 24-28” 60-72 cm

2) Measure Your Child’s Height and Inseam

The next thing to do is to measure your child.  Don’t skip this step or guess!

If you’re buying the bike as a gift, you should still be able to ask the child’s parents to measure them for you.  Lie and say you’re sewing clothes or something if it must be a secret!

Measure your child’s inseam AND their height.  You’ll want to take the measurements in inches (or convert to inches once you’re done). 

To measure your child’s inseam, have them stand against with their back against a wall, legs together, and place a book between their legs. Have them hold it as close to their crotch as possible. Then, using a pencil, mark where the top of the book hits the wall.

Make sure to write down those measurements and save them for our next step.

3) Look Up the Specs for the Bike (or Bikes) You are Interested In

Just because you think your child probably needs a 14″ bike doesn’t mean that ANY 14″ bike will fit them.  Different bikes have different stand-over heights and min/max seatpost heights.  It’s best to look for a bike that will provide the BEST FIT for your kiddo.

Not all bike manufacturers list the standover height for their bikes.  If they do, however, you should compare it to your child’s inseam.

The standover height is the height of the top tube of the bike frame where your child will be positioned when standing with one leg over each side of the bike.  This means that your child’s inseam needs to be AT LEAST as tall as the standover height.  Ideally, there will be a little more space than that for your child to maneuver the bike comfortably.

Prevelo Alpha Three Kids Bike
Your child needs to be able to comfortably stand over the top tube of the bike

The other stat that you should absolutely look up is the minimum seatpost height for any bike you are considering.  How the minimum seatpost height compares to your child’s inseam is dependent on whether you are buying a balance bike, first pedal bike, or a pedal bike for a confident pedaler.

For a balance bike, you want to make sure that the minimum seatpost height is no higher than your child’s inseam length.  This allows your child to put their feet flat on the ground, to learn to balance and to scoot.

So if the bike has a 12″ minimum seatpost height, then you need to make sure that your child has at least a 12″ inseam.  If not, look for a bike with a smaller minimum seatpost height.  

For a balance bike, you want your child to be able to place their feet flat on the ground while sitting on the seat.

If you are buying your child’s first pedal bike, then you want to make sure again that your child’s inseam is at as long as the minimum seatpost height or no more than 1″ apart.  This is because kids who haven’t learned to pedal yet, will want to be able to put their feet flat on the ground.  This gives them stability and the ability to “scoot” if they feel so inclined.

If your child already knows how to pedal (sans training wheels), then you can choose a bike with a minimum seatpost height that is 1-3″ higher than their inseam length.   This allows your child’s toes to touch the ground but not put their feet flat on the floor. 

islabikes beinn 20 size
This confident rider is at the small end of the size spectrum for this bike but is still able to comfortably reach the ground.

DO NOT buy a bike that has a minimum seatpost height any higher than 1-3″ longer than your child’s inseam.  They will not be able to touch the ground, will struggle to reach the pedals, and are probably going to struggle or get hurt. 

There are two ways to look up all information like minimum seatpost heights.  Your first option is to go directly to the manufacturer’s website.  Any decent brand is going to provide specs for their bikes.  If they don’t, don’t waste your time with their bikes.

Some manufacturers have even created special tools to help you pick the correct size bike for your child.  The Woom Bike Quiz or the Guardian Bikes RideSizer tool, for instance, helps you determine which size bike your kiddo needs online.  

woom size chart
The Woom size chart makes picking the correct size bike easy!

Your other option is to use one of our comparison charts.  For each child’s bike size, we’ve rounded up a list of some of the best kids bikes available and included a comparison chart with this info for you.  This is a quick and easy way to see which bikes will best fit your child.  

Balance Bike Guides & Comparison Charts:

Pedal Bike Guides & Comparison Charts:

What To Do When Your Child Is In Between Sizes

It’s pretty easy to choose a bike when your child fits nicely at the bottom end of the recommended height/inseam for a bike. It’s tougher when your kiddo is at the the upper end of the recommended height/inseam for a bike.

When this happens, we hear from lots of parents that they are worried that the bike won’t last very long, and that their child will outgrow it quickly. This is a valid concern, since neither bicycles nor money grow on trees.

If your child is pretty dang close to the next size bike, I generally tell parents to go ahead and size up. This is especially true if your child already knows how to pedal and is a confident rider.

You know your kiddo best. Are they athletic and capable of handling a bigger, heavier bike? Are they going to be confident standing on their tippy-toes or are they going to be scared?

If your child isn’t already a whiz on the bike, then consider staying on the smaller size bike, even if they will outgrow it soon. In this case, you might want to look for a used bike (or borrow a bike from a friend). You can buy an expensive bike several months down the line after they’ve had a bit of a growth spurt and are ready for the next size bike.

A Word On Kids BMX Bike Sizing

And now to throw a wrench into everything I’ve said above. If you’re buying a kids BMX bike, the above rules on bike size don’t apply.

There are two different types of kids BMX bikes: freestyle/street BMX bikes (that you would use at a skatepark for instance) and racing BMX bikes (which you would use on a race track). Both have different sizing.

For freestyle/street BMX bikes, you’ll generally want to choose a bike that has a wheel size one size smaller than you would for a traditional kids bike. In other words, if your child would ride a 16 inch bicycle, they’d want a 14 inch BMX bike.

Learn More:


For kids race BMX bikes, the wheel size is always 20 inches–even for really tiny riders. Only the frame size changes as your child grows.

There are five sizes of kids BMX racing bikes:

  • Micro Mini (under 5)
  • Mini (5-7)
  • Junior (7-9)
  • Expert (9-11)
  • Expert XL (10-13)

And here’s how they are sized by your child’s height:

Micro Mini<53’6″-4’0″
Expert XL10-135’3-5’7″

Why Size Isn’t The Only Thing That Matters

Yes, size is the first thing to think about when picking out a kids bike but it certainly isn’t the only thing that you should be thinking about.  Once you know what size bike your child needs, you should begin thinking about things like weight (this one is a biggy), geometry, brakes, tires, whether or not to use training wheels, etc, etc, etc.

For more information on other things you should be considering, read our Guide To The Best Kids Bikes & How To Choose!

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    About Us

    The Rascals are a family of three. Kristen (mom), Blair (dad), and Parker (kiddo). We started Rascal Rides when Parker was born and we didn’t want to give up our passion for biking. As we learned, we shared. Over the years, we’ve tested hundreds of kids bikes, helmets, bike trailers, and more.

    Kristen is a USA Cycling certified coach and loves to share her passion for biking with other families. Blair is a bike geek, mechanic, and mountain bike junkie. Parker is our resident tester and inspiration.

    If you see us out on the trail, make sure to say hi!

    69 thoughts on “Ultimate Guide To Kids Bike Sizes (And Bike Size Chart!)”

    1. lost me when i saw you were using some antiquated, outdated, stupid units of measured. Its called the metric system people. 90 percent of the world uses it. oh hang on let me do some conversions. No I will just look elsewhere

      • 90%?? A big chunk of those would have to convert the text (English) to the language they read, would they not?
        No where near 90% of English readers use metric, maybe half that.

        • Math has no language barriers. (Speaking from experience). 90% is right.
          – the number is likely higher.

          Still not worth the previous reaction.

      • So, finding another source will take you less time than applying some second grade arithmetic? Oh, hang on, I get it now. It’s not about your convenience. You imagine that the writer of this page will feel your scorn and change his ways. In the future, when trying to take the intellectual high-road, you should have someone knows some English proof read your post before submitting it.

        • Let’s all be reasonable…15cm sounds like it will be a lot longer than 6in if one is asked on certain websites.

      • Get that chip off your shoulder Steve. A lot of people don’t agree with you. Even if you are right you are going the wrong way about receiving agreement!

      • unfortunately many countries around the world have converted to the imperial (U.S.) system, away from metric. And bikes in the U.S. are still built around the Imperial system, so if you cannot understand inches and foot measures, it is best you do not buy a bike in the U.S.

        • Idiot, imperial measurements a US system? It’s in the title, imperial like the British Empire what ruled a massive chunk of the world! For those of us born in 1960, we used the British Imperial measuring system (feet and inches, pounds shillings and pence, ounces, pounds, pints and gallons and much more until we went to “big school” we then learned the European Metric System. The modern world was built on the Imperial and hats off to the yanks for using it still.

      • I thought this information was offered so your child can learn and have fun. It’s pretty easy to figure out measurements, Steve. I hope your kid doesn’t wind up being a “stupid unit” like you. Best of luck!

      • Yet you thought it was important enough to waste your time to come here and complain to a bunch of people who don’t care and think you are an asshat. Hey news flash dumbass, if you are buying a kids bike in the U.S. it is most likely going to be sized in inches so this article is perfect as is. If you don’t like it then move along but don’t feel the need to cry to us next time because you are too stupid or lazy to do a simple conversion.

      • Really? Ok Karen, thanks. Last time I checked… the Signs in my state say 70 MPH….. My tape measure is also in INCHES. Lumber is sold by the FOOT and meat by the POUND. If I were this company I would hope you absolutely looked elsewhere.

      • ISO metric bike site that also points me to a metric bike store so I don’t have to convert back to imperial units. Asking for a “friend”, his name is Steve 🙂

    2. Wow! Some people can be so rude! How about this? If you don’t like what the article says or the measurement system or conversions it suggests, then don’t read it! Find another! Negativity and ignorant comments should be left inside your home! Other readers are appreciative of the time the author took to write these helpful tips. People like you with your exhaustive and pathetic comments are a waste of oxygen! Keep to yourselves.

    3. My tiny 6 1/2 old, 108 cm height, 48 cm inseam, this month started riding Islabikes Beinn 20 Large (I believe this is 12 cm below catalogue suggested body height), leaving just-in-size Cnoc 16 dusted. ‘I’d like to ride those big wheels today, Daddy’. So you never know…

    4. I’m here due to quarantine 2020. Anyone else?! HA This video was very helpful! Especially since it is more difficult to shop in the stores. Now I feel like I can order a bike online for my son with confidence. Thank you so very much!!

    5. Still in quarantine here, and I’m so happy I found your site. My daughter, who has always been afraid to ride, got brave in March while we were starting our shelter-in-place. We felt like she outgrew her bike, and now we know for sure she has. Thank you for all of this helpful info!

    6. Thank you! I have 99%ile in height 5-year old who is getting her first bike. Her legs have grown at least three inches since March. Since we can’t go to the store and try out bikes, I really need to figure this out. You have helped immensely.

    7. Hi, do you have any recommendatiosn for picking a bike for an 11 year old boy (almost twelve), he is 5’1″ and inseam is 28″

    8. My son is 4 year old (41″ height, 17″ inseam). He enjoys his balance bike and never learn to pedal. I am little confused if I should go for 12″ or 14″ bike (mainly to teach him to pedal)? Any suggestions ?

    9. Thank you so much for the useful information . The video is very clear and helped me a lot choosing the right size (although i had to spend 3 seconds to ask Siri to convert the CM to inches jejeje)
      went with your list to the store, it was a success among other parents and even the sellers at the store asked me for it.
      One comment: The text area in the above “insert email” box is white so one cannot see if he is entering ones email. i assume its a fixable bug to change the text to black.
      again, thank you.

    10. Folks – I’m confused what to pick because my daughter is fast growing and the chart above doesn’t help me. Which would you pick for her height of 3’9″ and 16′ inseam

      • Hi George, You might want to double check her inseam. A 16″ inseam sounds pretty short for a kiddo that’s 3’9″. If that really is accurate, I’d go for a 16″ bike with a lower standover height (like the Prevelo Alpha Two, for instance).

    11. Shouldn’t the inseam be taken with the child wearing the shoes they would typically ride in? The video suggests barefoot.

    12. Thank you for this article, I followed your instructions and had the kid sit on the bike before I bought it. I have a lot of time on my hands too, so I baked some cookies for Steve. Steve needs a cookie.

    13. hi my name is andrew and you dont have my age on your board and now i can’t find my tire size but yet you have all this reading that no one wants to read

    14. Thank you for this AWESOME information! I was able to find a great bike for my 6yo (22″ inseam), a used Raleigh Rowdy 20 6-speed for $80, and bought it with confidence knowing that it would fit based on your recommendations and measuring guide.

    15. I’m lost. When did Inches and Centimeters become antiquated, outdated, and stupid? Aw, Napoleon…..sounds like you didn’t quite measure up to the standard.

    16. I will assume we’re here because we love the kids in our lives…not squabble like them. (I’m no better…I catch myself being pretty silly over silly things, too).

      1 inch = 2.45 cm, btw.

      • Sorry, you got the numbers in the wrong order after the decimal point.
        1 inch = 2.54.
        That said it won’t make a huge difference.

    17. Hello! I know this guide is a couple of years old but I’m hoping you’ll get this & reply. I have a 10 yr old son (August of this year) who’s 4’4” with a 23-23.5 inseam. So he’s probably on the shorter side. New rider. What brand of bike would you suggest? Would you go with a 20” wheel? Thank you in advance, Mia

    18. Hi Kristem!
      I am looking for a bike for my nephew. He just turned 7 but he is quite tall 130cm and his inseam is 60cm. I think he may be on the border between 20″ and 24″..not sure what size to get. Could you help?

      • Hi Marta,
        I would definitely go with the 24″ bike. Just make sure to compare his inseam to the minimum seatpost height on the bike you choose. Some 24″ bikes are smaller/bigger than others.

    19. Hi Kristen – thanks for a very helpful article. Just thought I’d take you up on some individualized advice. My daughter will be 7 in February and only has experience with a bike with training wheels. She’s 44″ (3 ft, 8 in) and 22″ inseam. Based on the article and the charts, my sense is that 16″ wheels would work but she’d outgrow it fast, and 20″ is probably doable, but a little bit of a stretch right now, and 18″ is “just right” (goldilocks-style). Do you agree? We’re just gonna go with an off-the-shelf Target or Walmart bike, so not planning on anything fancy, and happy to get her something more pricey/better down the line. I noticed that 18″ is less available though. If I can’t land on an 18″ (and if you agree that’s the best fit), should I go 16″ or 20″?

      • The frame size will matter more than the wheel size and will vary a lot from brand to brand. If you are for sure planning a big box bike I’d get a Schwinn Elm 18″ which ought to be a perfect fit, could order online too.

    20. This is quite possibly one of the most depressing things I’ve read all year. While I agree about WalMart bikes, you’re doing a lot of people an enormous disservice by only recommending very expensive bicycles. The message that you’re delivering is that only the wealthy can safely enjoy one of the few covid-free activities left. Because unless a parent has many hundreds of dollars to drop on an exclusive bike brand, nothing is safe or even enjoyable.
      Really kind of crappy.

      • Hi Marybeth,
        I understand what you’re saying, and that’s definitely not my intent. If you spend much time on this site, you’ll find that I frequently say “any bike is better than no bike.” Also, I’m a huge proponent of buying kids bikes used. My gripe is simply with parents that will spend $500 on a new video game console, but not $500 for a decent bike.

    21. According to your chart my son looks to fit the 14″. He is 3ft 4 and 1/8 inch tall and 17 inch inseem. He will be 5 next month. Wanting to get a bike with training wheels. I’m anticipating a big growth spurt over the next year. He hasn’t grown much in the past year. Do you think he’d handle a 16″ training wheel bike? Thanks.

    22. Thanks for the information

      We are on shut down again and wanted a bikevfor our grandson.
      I could order one
      Your article is very helpful.

    23. Hello! Thanks so much for taking the time to put this article together..super helpful!

      The problem that I am having is that, like you had mentioned, my daughter is on the cusp of sizing up a bike size…she is almost 10 and appx 4’5 and 65lbs…so on the high end of a 20’’/low end of a 24”…but she is also still new to riding and is still learning the basics so I am uncertain about which size would be the best fit for her? Any suggestions? Thanks so much!!! 🙂

      • If you had any suggestions both for the best sizing of a regular bike for her size, as well as bmx sizing, that would be super helpful. Thanks again!!


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