Let’s start with the truth: there’s no such thing as a universal “true to size” in footwear. Shoe sizing isn’t standardized because manufacturers use different lasts—the forms used to shape shoes. These vary by brand, model, and even gender or age group, which means a size 10 in one brand might fit very differently from a size 10 in another.

Finding the right size Run 619 insole is straightforward. The best way? Measure the length of your current insole from heel to toe and compare it to our sizing chart. Choose an insole that matches or is slightly longer (never shorter)—you can always trim the front edge for a custom fit.

No insole to measure? Use your foot. Measure from your heel to your longest toe, then add a little extra length—about a thumb’s width—for ideal spacing in your shoe.