p90x with bands

Just wondering, how do I know how many pounds of force I am lifting with the Aylio Resistance Bands?

I’m starting P90x with these bands. I know that each color band has a set amount of strength, ex: Black(Ultra heavy), but I’m not sure exactly which bands to combine for a set workout or precisely how many pounds of force is exerted?

I asked alyio this question and they responded with:
Black is 20 pounds
Yellow is 15 pounds
Red is 10 pounds
Blue is 5 pounds

Hope this helps.

By the way how are the bands in terms of quality?