The ASBC has no MOA (Method of Analysis) for subjective analysis of sweetness but there are MOAs for Reducing Sugars and Total Carbohydrate.
In other industries subjective sweetness is judged by comparison to standard sucrose solutions of strength up to about 15%. If a 3% solution of sweetener x is judged to be as sweet as a 9% solution of sucrose it is said that sweetener x is three times as sweet as sucrose. And so on.
There is also degrees Brix which is used to describe the amount sucrose by weight in an aqueous solution. 1dB = 1g sucrose in 100g aqueous solution.
"I'm a glass half-empty kinda guy. When it's half full, that means you're filling it, like a bartender. When it's half-empty, that means you're drinking it. I'd much rather be drinking the beer than pouring it."
The Bx (degree Brix) is not a measure of sweetness nor is the °P (the near equivalent and the unit used in brewing). They are units of mass concentration. A 1.73 °P (1.73 Bx) solution of sucrose will taste as sweet as a 1.00 °P ( 1.00 Bx) solution of fructose because fructose is 1.73 times sweeter than sucrose.