I have some of the powdered stuff (the blue box) which says to mix with water at 1:20 by volume for household use, 1:10 for heavy-duty, and 1:4 for ultra-heavy-duty.
OP says to mix 2 tablespoons with 8 cups of water (total) which is 1:10 so I guess this is heavy-duty strength. Makes sense. (2 tablespoons = 1/8 cup)
The use-cases on the liquid stuff don't quite line up with the use-cases on the powder, in terms of what's considered heavy-duty or ultra-heavy-duty or whatever, but they range from 250 mL in 4 L (1:16) to using it straight, i.e. 1:1.
If we assume 1:1 liquid is the same strength as powder mixed at 1:4, then you need 4x as much liquid for the same volume of water. In other words, if you need 2 tablespoons of powder for 8 cups of water, then to get the same strength you need 8 tablespoons of liquid = 1/2 cup.