Helmet Size Conversion Chart - Up North Sports Helmet Size, Hat Size, Head Circumference - Inches, Head Circumference - Metric. 2XS, 6 3/8 - 6 1/2, 20- 20 1/2, 51-52. XS, 6 5/8 - 6 3/4, 20 7/8 - 21 1/4, 53- 54.
