Chaco Z1 Eco Tread Sandals Women's Size 9 Men's Size 8 Used- Some wear- Torn back strap on back of Left sandal I am not sure about the size on the back heal it could be a 6 or a 9. It doesn't have a W or M. The measurement is approximately 10.25" (see pic). I have posted a pic of the size chart for Chaco's for Men and Women converted from inches.