The method of measuring enzyme potency differs from what many people are accustomed to. It is not the quantity of the ingredient (in mg or IU) that counts, but rather the quantity of food that an enzyme can break down or digest that determines an enzyme's potency. The potency of enzymes is not measured by weight, and thus a measurement in mg or international units (IU) would not describe the true potency of the product. Activity units (e.g. SPU for Serratia peptidase, as an example) are the most commonly used measurement to determine potency because they identify how active the enzyme is, and allow you to accurately compare the potency of different products containing that enzyme. An 'active unit' (e.g. SPU) is a measurement that describes how much of a given food an enzyme has the potential to break down.
For example, two products could both contain 100 mg of Serratia peptidase in a tablet, but if one has, let’s say, 100 SPU/mg potency while the other has 50 SPU/mg, then the former will be twice as potent yielding 10,000 SPU vs 5,000 SPU per tablet.
For any product that lists ONLY milligrams or IU on the label and NOT also the enzyme activity units (e.g. SPU), you will need to find out from those manufacturers what is the potency in enzyme activity units per mg (e.g. SPU/mg) for the enzymes in their product.