How to Fit a Kids Bike Helmet

While it’s always great to see kids wearing a helmet, if that helmet doesn’t fit correctly, then your child isn’t receiving the protection that they should have. An ill fitting helmet–one that’s too big or too small, moves side to side, or tilts back too far–isn’t that much safer than no helmet at all.

The good news is that it’s not that hard to fit a helmet properly. With a few tips and a little bit of time, that lid will be safe as can be.

In this article, I give you five steps to make sure that your child’s helmet is fit properly and providing maximum protection.

Step 1: Make sure the helmet is the right size.

It seems obvious, but I see lots of kids wearing helmets that aren’t even the right size.  There is no way to adjust a helmet to make it fit if it is way too big (or small) for the kid.

To size your child for a helmet, you want to measure their head circumference.  You can do this with a cloth measuring tape (easiest option), or by using a string and then measuring it against a ruler. 

Measure around your child’s forehead, just above the eyebrows.  Make sure to measure in centimeters or millimeters (or convert from inches to metric after the fact).

You can then compare this measurement to the helmet manufacturer’s sizing table and pick an appropriate helmet for your child (or verify that their current helmet fits).

If for whatever reason you can’t physically measure the child (for example, maybe you’re a grandparent buying the helmet as a gift), you can use the below table as a general guideline.

AgeHead Circumference (in cm)
12 months46
2 years48
3-5 years51
6-10 years53
11+ years56

Step 2: Make sure it is snug.

Helmets are designed to last for a while which means they are usually adjustable.  To make sure the helmet fits your child, the helmet will come either with multiple helmet pads or a rear fit dial (or both). 

With skate-style helmets and cheaper helmets, you generally have to rely on padding.  Other cycling helmets will have a rear fit dial at the back of the helmet that tightens or loosens the helmet.

giro tremor dial adjust

Compared to padding, fit dials do a superior job of tightening the helmet and getting a good fit. If you’re shopping for a helmet, I’d highly recommend choosing one with a rear fit dial.

The helmet is appropriately snug when your child can shake and roll their head without the helmet shifting.  The front should be aligned just above your child’s eyebrows (that same place where you measured their head circumference).  If it is tilted backward and you are seeing large expanses of their forehead, it is either too large or needs to be tightened.

The helmet on the left is titled too far backward (photo credit). The helmet on the right is positioned correctly right over the eyebrows.

At this point, I also like to ask the child how it feels.  As parents we are often eager to make sure it is REALLY tight, but you also don’t want it so snug that it hurts.  If the helmet is uncomfortable, the child won’t want to wear it.

Step 3: Adjust the side straps.

The straps on either side should come to a Y just below your child’s ear.  I generally find this easiest to accomplish by adjusting it while they have the helmet on their head.  That is, if they will stay still long enough for you to do it.  Good luck, mom!

Side straps appropriately adjusted
This helmet is fit perfectly! Photo credit.

On most helmets you’ll have to make this adjustment manually, though some helmets have adjustment-free side straps which make this a cinch.

giro tremor helmet coverage 2

Step 4: Adjust the chin strap.

Tighten the chin strap so that it is snug but not excessively so.  You should be able to fit one finger between the strap and your child’s chin, but no more.

In the photo on the left, the chin strap is far too loose. In the photo on the right, the chin strap is adjusted appropriately.

Depending on the design of the helmet, there might be some extra length of strap just hanging out.  If this happens, I like to trim the strap so that there is 6 inches or so remaining, and then fasten the remainder in place with a rubberband.

Step 5:  Keep checking.

Adjusting your child’s helmet once isn’t enough.  If your kiddo is like mine, they will tug on the chin strip until it loosens and play with the fit ring on the back of the helmet. 

Keep an eye on the fit.  Is the chin strap loose?  Is the helmet crooked on your child’s head?  If so, it’s time to tighten things back up. 

I make sure to do this a couple times a month, and more often if needed.

Other helmet safety tips

  • If the helmet has been in a crash, or if it has been dropped, then it needs to be replaced. Even if there are no visible signs of damage, the integrity of the helmet may be damaged.
  • Teach your children to treat their helmets kindly. To the point above, if your kid throws their helmet or lets it carelessly fall to the ground, the helmet is getting damaged and won’t be as effective in a crash.
  • Check the helmet for visible signs of wear. I was recently looking at one of my son’s helmets and noticed there was a crack in the foam!!  Time to throw that baby out!
  • My favorite helmets for kids are ones with MIPS-technology. These are more expensive but provide superior protection.
  • If your child is into multiple sports (skateboarding, skiing, etc) don’t just assume their existing helmet will work for biking too. Make sure that it has a CPSC label certifying it for use on a bicycle.
  • Store the helmet indoors. Extreme temperatures (both hot and cold) can damage the helmet.  You also want to keep it away from direct sunlight.
  • We all know kids are dirty. To clean a bike helmet, use warm water and mild detergent.  Avoid soaking the helmet or exposing it to high heat.

Now That You Know How to Fit a Helmet, Choose The Best One For Your Child

18 thoughts on “How to Fit a Kids Bike Helmet”

  1. Your third bullet point in the ‘Other helmet safety tips’ is something I am hesitant to agree with. If there’s a crack in the helmet you say ‘throw that baby out’. Seems a bit harsh. Maybe keep the baby and spend money on a new helmet :).

    Great, helpful article. Thank you!

  2. Please update your photos on your bike helmet fitting page as they promote a poor fit. Only the boy pictured in the red Bell helmet has a good fit.

    Bike helmets should sit at most two finger’s widths above the eyebrows. Many of your pictures show overexposed foreheads. An exposed forehead means a hit to the frontal lobe of the brain.

    Thank you


    • Did you read the captions Sandi? I specifically showed photos of both good and bad fit with captions so people would know what not to do as well as what to do.

      • Hi 👋🏻 Just wondering if you have any thoughts on what I can do for a super tiny head. My almost 2yr old has a head circumference that is 43.5cm. All 3 of my kids have tiny heads…1st-3rd percentile. I can’t find a helmet in Australia for <46-52cm 😕 Is it safe to add padding to fill it out?? He is starting to hoon around on his scooter and I can’t find any info on how I can protect his tiny noggin. Any thoughts?

        PS thank you for this article…think I need to check the other kids’ helmets too 🙈

        • Hi Kristy,
          That is tiny! I’d try the Giro Scamp. In my experience, it fits heads a little smaller than advertised if you tighten the dial all the way. Same goes for the Lazer P’Nut.
          Let me know how it goes!

      • I can see why Sandi thought that. There is an add between the picture and the caption. Thanks for showing the comparison. I see kids wearing them incorrectly. Appreciate the info. Thanks heaps

  3. Hi Kristen,
    I’m having trouble picking a helmet for my son. I’m interested in the Giro dime mips but i’m worried it might be too heavy for his neck in the event of impact. He has a large head and is only 3 so I’m worried that the youth S is more for the neck strength of an 8 year old even though the head circumference fits my 3 year old. What is the maximum weighted helmet a toddler should have? Your blog is the only reviews I’ve found that show the weight of helmets on your comparison chart. Thank you for being so thorough and clear in your process.

    • Glad to help Olivia. From a safety standpoint, I don’t think there are any clear guidelines on weight. From a comfort standpoint, however, I do think the Giro Dime MIPS would be a little too heavy. Is there are reason you are considering that specific helmet? The Giro Hale MIPS or Giro Tremor MIPS for instance are quite a bit lighter.

  4. Hi Kristen, wonder if you’ve tried the Abus Mountz and what your thoughts are between Abus Mountz and Giro Tremor MIPS. We have the Abus Mountz, which fits well on my 5yo but I’m thinking of getting the Tremor MIPS because of all the rave reviews I’ve been reading. But wonder if I should get another one since the Abus (I have the option of returning) is comfortable and fits well.

    Also, would you happen to know how different the fit is between Giro Tremor MIPS and the non-MIPS version? I only have access to try the non-MIPS version.

    Thank you!

    • Hi Germaine,
      I have not tested the Abus Mountz so I can’t speak to it I’m afraid. That said if the fit is good and you love it, I wouldn’t mess with a good thing!

      The fit between the MIPS and non-MIPS are virtually identical.



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