1:The way to choose perfect shoes for your children. Foot length+10MM=Inside Length. Such as Pls measure your kid's foot length as below.IF her/his foot length is 165MM,you can add 10MM. That's to say,choose inside length 175MM.Thank you for your support. 2:Because of different measuring methods,there may be about about 10mm error,belongs to normal. 3.If you feel difficult to choose the size ,you can feel free to contact me we will give you some suggestion.