This chart is not the most accurate but one of the easiest.

Figure your horse's weight using this handy chart! All you need is a regular tape measure, no special equipment required. Measure the "Heart Girth" as in the picture below:

Heart Girth (")   54     56      58     60     62      64     66      68      70      72       74      76

Weight (Lbs.)   492   531    596   664   722    785   852    902     985  1065   1225   1265