Hi Karen. Subtract the new weight from the original weight. Then take that value and divide it by the original weight. Then multiply by 100.
For example, if you have a barrel of coffee beans that originally weighed 120 lbs and after now it weighs 90 pounds:
120  90 = 30
30 / 120 = 0.25
0.25 * 100 = 25%
Hope this helps!
Stephen La Rocque.
