To measure your horse for an Active Suit or Travel/Recovery Suit, simply take a height and heart girth measurement. Height should be in hands (1 hand = 4 inches) from the ground to the tallest part of the wither with the horse standing square.
A Heart Girth measurement should be taken as the entire circumference of the horse's chest in a vertical line just behind the shoulder (where the girth/cinch lays). This measurement may not necessarily include the tallest part of the withers. Once these measurements have been obtained, refer to the chart to determine the size your horse needs.