7iDP Bike Helmet Size Chart

1. Achieve the perfect fit by measuring your head circumference correctly.

2. Watch the video below to see how to measure your head correctly. (If you don’t see a video below, please refresh this page, or you might need to allow this website through your Ad blocker.)

3. VIDEO: How To Measure For A Bike Helmet

4. On the chart below, find the helmet model that you are interested in, then find your head measurement to see which size you need.

7iDP Bike Helmet Size Charts

7iDP Mountain Bike Helmets Standard Sizing

Model Youth Medium Youth Large X-Small Small Medium Large X-Large XX-Large
M1 Helmet 48 – 50cm 50 – 52cm 53 – 54cm 55 – 56cm 57 – 58cm 59 – 60cm 61 – 62cm
18.8″ – 19.6″ 19.6″ – 20.5″ 20.75″ – 21.25″ 21.5″ – 22″ 22.5″ – 22.75″ 23.5″ – 23.75″ 24″ – 24.25″
Project 23 ABS

53 – 54cm 55 – 56cm 57 – 58cm 59 – 60cm 61 – 62cm 63 – 64cm


20.75″ – 21.25″ 21.5″ – 22″ 22.5″ – 22.75″ 23.5″ – 23.75″ 24″ – 24.25″ 24.8″ – 25.2″
Project 23 Carbon

53 – 54cm 55 – 56cm 57 – 58cm 59 – 60cm 61 – 62cm 63 – 64cm


20.75″ – 21.25″ 21.5″ – 22″ 22.5″ – 22.75″ 23.5″ – 23.75″ 24″ – 24.25″ 24.8″ – 25.2″
Project 23 Fiberglass

53 – 54cm 55 – 56cm 57 – 58cm 59 – 60cm 61 – 62cm 63 – 64cm


20.75″ – 21.25″ 21.5″ – 22″ 22.5″ – 22.75″ 23.5″ – 23.75″ 24″ – 24.25″ 24.8″ – 25.2″

7iDP Mountain Bike Helmets Sizing #2

Model X-Small / Small Medium / Large X-Large /
2X-Large
M2 Helmet 52 – 55cm 56 – 59cm 60 – 63cm
20.5″ – 21.75″ 22″ – 23.25″ 23.75″ – 25″

7iDP Mountain Bike Helmets Sizing #3

Model Small /
Medium		 Large /
X-Large
M5 Helmet 54 – 58cm 58 – 62cm
21.25″ – 23″ 23″ – 24.5″