system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 Stevia is 100+ times sweeter than sugar. How is sweetness/taste measured?
gpt
Taste threshold.

We know that, to detect sweetness, you need about an 0.5% concentration of sugar (or more specifically, sucrose, the sugar you buy in bags at the store) in water. Below that, you won't notice it being sweet; above that, you'll notice progressively stronger sweet sensations. For comparison, a 12 fl oz can of Coca-Cola (listed as 355 mL and thus 355 grams, give or take, since it's mostly water) contains 39 grams of sugar, so coke has a concentration of about 11% sugar (though much of that sugar, at least in the US, is fructose, which is about 1.7x sweeter than sucrose).

Now, imagine you have a new substance you want to test. You try the 0.5% concentration, and people can taste it - so it's at least as sweet as sugar. You try 0.4%, still works. 0.3%, 0.2%, and so on. And finally, at 0.05% concentration, people stop tasting it. Since the threshold is 10x lower than the threshold for sugar, we say this substance is 10x sweeter.