What is the 2-2-2 rule for riding helmets?

I've never sat on a horse, but "is there a rule for how a helmet should sit?" is one riders do ask, so let's start with the number everyone repeats. The 2-2-2 rule is a three-point helmet fit check that comes from the bike-helmet world, not from riding. The American Medical Association's helmet-safety page describes it as one recommendation for checking that a helmet fits, and the helmets it covers are bicycle, e-bike, scooter and motorcycle helmets.

Its three checks, as the AMA page words them: the rim should be no more than two finger breadths above the eyebrow; there should be two fingers' width of space where the side straps meet the ears, with the straps sitting just below them; and there should be room for two fingers under the chin strap.

Safety is the business of standards bodies, doctors and helmet makers, so on this page we're passing along what they say and not offering a safety verdict of our own. One thing we could not find: the riding sources we read (the CDC's equestrian helmet handout, Troxel, Trauma Void, the Government of Alberta, Utah State University Extension and our own Helmet Buyer's Guide) describe similar checks in their own words, and none of them uses the name "2-2-2."

The table puts the AMA's version beside what the riding sources we read say.

Notice that the brim is described three ways: two fingers, about an inch, and no more than an inch and a half. Troxel itself calls the spot about one inch, roughly the width of two fingers. Fingers vary and inches don't, so if your helmet maker's fit guide gives a number, use theirs.

Here is what the sources say, in their own order of importance as best we can tell.

The CDC's handout, written for parents of young riders, says an equestrian helmet should fit snugly all around, with no spaces between the foam or padding and the rider's head. It adds that the back of the helmet should not touch the top of the neck and that you should be able to see the rider's eyes and the rider should see straight ahead and side to side. For the chin strap it describes a yawn test: ask for a big yawn, and the helmet should pull down on the head; if it doesn't, the chin strap needs to be tighter. Once it's fastened, the CDC says, the helmet should not move in any direction.

• Troxel: shake your head. If the helmet doesn't move, that's a good sign.
• Government of Alberta (page reviewed 2018): bend forward and shake your head up-down and side-to-side; the helmet should not slide. Ears should not be pressed on.
• Trauma Void: a mirror test. Hold the helmet with both hands and rock it gently; if the skin on your forehead follows the helmet, the fit is proper, and if the helmet moves but the skin doesn't, it's probably too big or too oval for your head.
• CDC: ask the rider how the helmet feels. It needs to be snug, but one that is too tight can cause headaches.

They're separate questions, and the sources treat them separately.

The Government of Alberta page says to make sure any helmet you try on is certified ASTM/SEI or BSI, and Utah State University Extension says to look for ASTM and SEI certification. The Safety Equipment Institute's site says its programs are based on globally recognized standards including ASTM, and lists US Equestrian and the United States Pony Clubs among the organizations that mandate certification to ASTM standards. Our helmet ratings page adds a contrast with the bike world: riding helmets aren't federally regulated the way bike helmets are, a certification is pass or fail, and it says fit and certification work together.

Where is the tag? Our helmet ratings page says the certification label is usually under the liner or on a sticker inside the shell, and lists four things to read on it: the standard's name, the version year, the quality mark (such as an SEI seal) and the date of manufacture. It also notes that most makers recommend replacing a helmet roughly every five years and after any fall where it takes a hit. Our replacement page has more.

If you show, check your discipline's rule book as well; our show-ring helmet page collects what the federations say.

The CDC says to try the helmet on with the hairstyle that will be worn while riding, since fit can change if the style does; a long-haired rider who gets a very short haircut may need to adjust the fit. IRH says trying it on with your hair styled as you'll wear it is the best way to make sure it fits properly. Our braids, locs and protective styles page goes into hairstyles.

Size and shape come first. Troxel measures about an inch above the eyebrows and says its chart is a guide, not a guarantee of fit, and that some head shapes call for a different size or fit one helmet better than another. Our measuring page walks through the tape, and our round or oval page covers shape. Some helmets have removable padding or a fit ring that can be adjusted, the CDC notes, for fine-tuning.

The AMA page quotes a physician noting that fit needs extra attention for children, since their heads are still growing. The CDC handout suggests bringing the rider along when you shop so you can check the fit. Our Helmet Buyer's Guide says to re-measure and re-check every season, and not to hand down a helmet of unknown history.

For the full rundown on sizing up for growth, see our child's helmet page.

None of this replaces the maker's own instructions, so read those first: Troxel, for one, says its size chart is a guide only, and that some head shapes call for a different size.

Before you order, check:

• Hair: try the helmet on with your hair the way you ride (CDC, IRH).
• Brim: level, about an inch above the eyebrows (CDC, Troxel).
• Side straps: a "V" under the ears (CDC, Troxel).
• Chin strap: snug under the chin; the CDC says no more than one or two fingers fit between chin and strap. If your maker gives a number, use theirs.
• Yawn: the helmet should pull down on the head (CDC).
• Shake: it shouldn't slide when you shake your head or bend forward (Troxel, Alberta, CDC).
• Comfort: ask how it feels. Too tight can cause headaches (CDC).