ON VS ASICS: SIZING
On and Asics do not size the same, and running shoe fit is about more than length. On: Narrow-to-medium fit; go up half in waterproof models. Asics: One of the roomier toeboxes in running; wide and extra-wide widths on core models. The short version — starting from your On size, keep the same number in Asics. That rule comes from fitting both brands in the shop every day, not from the brands' charts alone.
ON VS ASICS FAQ
US 9 in Asics. From any On size, keep the same number.
On: Narrow-to-medium fit; go up half in waterproof models. Asics: One of the roomier toeboxes in running; wide and extra-wide widths on core models.
About a thumb's width in front of your longest toe, standing. Feet swell on long runs — if you're between sizes for a marathon shoe, take the half size up.
Ask us. Tell us what you run in now and how the toe room feels, and we'll size you by hand — or check the full charts on our size guide pages.