Groundies generally run true to size.
If you're between sizes, we recommend choosing the larger one, since barefoot shoes are designed to offer a bit more room.
Some people like having around 12mm (≈0.47 inches) of extra space in front of the toes for the ideal barefoot feeling, while others are comfortable with a little less (about 5–10mm or ≈0.2–0.4 inches).
As long as your foot stays securely in place, and you have good support through the midfoot, the fit should be just right.
To help you find your perfect size, check out our guide on how to measure your feet: 'How do I determine my shoe size?'