Inside length 21: 13.3cm, 22: 13.8cm, 23: 14.2cm, 24: 14.7cm, 25: 15.2cm, 26: 16cm, 27: 16.8cm, 28: 17.3cm, 29: 17.8cm, 30: 18.2cm

Because the shoes are not USB-connected, they are powered by a battery in the sole. Sometimes, due to the battery's charge, the light may not work, or one light may be brighter than the other, or one may be brighter than the other. All of these are normal. If there are issues with the light, such as one side being brighter or darker than the other, or if one light is brighter or darker than the other, or if the color is not even, we will not treat these as quality issues. People who are sensitive to these issues should be cautious when buying!