• Measure horse from point of chest to point of croup in inches (length of horse).
  
  
• Measure horse's circumference or heartgirth in inches.
  
  
• Calculate weight by the following: (heartgirth x heartgirth x length/300) + 50 = weight.

Example: If the Heartgirth is 70" and the Length is 65"
Step #1: 70" x 70" x 65" = 318,000
Step #2: Divide 318,000 by 300 = 1061.6
Step #3: Then 1061.6 + 50 = 1111.6
Horse weighs approximately 1111 pounds (plus or minus 3%)