Bicycle Helmet Safety Institute

Bicycle Helmet Size

Summary: How to measure your head for a bicycle helmet, including a helmet size chart with US hat size matched up with head circumference.

To find your approximate helmet size, measure around your head just above the eyebrows and use the table below. This is an approximate chart. Manufacturers do not always use the same size labels for a given circumference, and some are creative with small/medium or medium/large labels.

In addition to sizes, helmet shapes vary among manufacturers. You will have to try the helmet on to determine if it fits the shape of your head. A helmet that is fitted and adjusted properly should feel snug but not tight, and should not move from side-to-side or front-to-back. Expect to spend a good fifteen minutes playing with fitting pads and straps to get the best fit. You will be repaid for years with a comfortable helmet. We have some advice on fitting if you need it.

Sizing

Hat Size	Circumference (Inches)	Circumference (cm)	Approximate Size
XXXXS	18.11	46.0	Smallest helmets made.
XXS	18 1/2	47.0	Toddler
6	19	48.3
6 1/8	19 3/8	49.2
6 1/4	19 3/4	50.2
6 3/8	20 1/8	51.1
6 1/2	20 1/2	52.1
6 5/8	20 7/8	53.0	Small
6 3/4	21 1/4	54.0	Medium
6 7/8	21 5/8	55.0
7	22	559
7 1/8	22 3/8	56.8
7 1/4	22 3/4	57.8	Large
7 3/8	23 1/8	58.7
7 1/2	23 1/2	59.7
7 5/8	23 7/8	60.6
7 3/4	24 1/8	61.6	Largest helmets usually available.
7 7/8	24 5/8	62.5
8	25	63.5
8 1/8	25 3/8	64.4
8 1/4	25 3/4	65.4
8 3/8	26 1/8	66.3	Largest helmet on our Big Heads page.
8 1/2	26 1/2	67.3	No known model.

See our page on big heads for more.