Calcium Chloride Dihydrate has a density of 1.85 g/cm3 so 1 gallon (128 fluid ounces) of Calcium Chloride Dihydrate should weigh 15.44 lbs (247.04 oz weight).

So 1 ounce (weight) of calcium chloride dihydrate should be 1.93 fluid ounces volume. 247.04/128=1.93

My calculation must not be correct because I see in Pool Math 10,000 gallons for a 500 ppm increase in CH it shows "981 oz weight = 1126 oz volume" whereas my calculation would be 981 oz weight = 1893 oz volume. 981 x 1.93 = 1893.

What am I missing?