We recommend using a soft tape measure. If you do not have a soft tape measure you can use something like string, wrap it around the fetlock, mark where the end meets the rest of the string and then simply lay it flat next to a tape measure,to get your measurement.
Be sure to measure both the FRONT & BACK fetlocks as they are often different sizes. It is ok to order boots in one size for Front and a different size for the Back
Small: 8.5 - 9.5 in. / 21.59 - 24.13 centimeters
Medium: 9.5 - 10.5 in. / 24.13 - 26.67 centimeters
Large: 10.5 - 11.5 in. / 26.67 - 29.21 centimeters
XL: 11.5 - 12.5 in. / 29.21 - 31.75 centimeters
XXL: 12.5 - 13.5 in. / 31.75 - 34.29 centimeters