The best measurements are taken from a harness you are using on the horse for whom the harness is being purchased. Even if it doesn't fit quite right, you will get more accurate measurements by measuring that harness and adding and subtracting from those measurements. For example, if the britching is 2" too short, measure the britching you have and add 4" (2" for each side) to get the length you need. If you are taking measurements off a harness, TAKE THE HARNESS APART AND MEASURE THE PIECES FLAT. The measurement will vary a great deal from a measurement taken "round" such as a browband still attached to the crown piece and curved. Use a soft, dressmakers measuring tape.