How do I measure for a Riddell SpeedFlex helmet?

Wrap a cloth tape ~2.5 cm / 1” above the eyebrows, take head circumference, and compare with the SpeedFlex size chart:

M ≈ 52–56 cm,
L ≈ 56–60 cm,
XL ≈ 60 cm+.
If between sizes, start with the smaller per Riddell’s guidance.