Packets of artificial sweeteners typically say something like “Sweet as 2 teaspoons of sugar”. Is this something that can be quantitatively measured in a laboratory? Or is it merely the consensus of the manufacturer’s taste-testers?
Many sweet things are measured in Brix, which is actually a measure of dissolved sugars. I don’t know of any sort of scale that compares sweetness between chemically different substances, though.
Scoville rating for hot peppers and the like was also defined based on human tasters. Nowadays, for capsaicin (the key ingredient in chili peppers), it’s normalized to the chemically-measured capsaicin levels, but you can still use human tasters to define a Scoville equivalent for other spicy chemicals.