Mixing Up H2Ocean Salt

[MMAX]

Noticed on the bucket everything in in pounds to gallons (1 pound of salt to 2.9 gal of water). If I don't have a scale what's the conversion to cups of salt to gallons? I'm mixing it into 20 gallons of water and the wife figured it to be about 12 cups of salt. I know IO salt is 10 cups to 20 gallons, the 12 cups doesn't seem quite right.