One pound will be equal to 453.59 mg while one cups will be equal to 236.59ml. Roughly you can estimate that 1 pound of water will be around 2 cups. Assuming the fluid is mostly water, the density should be 1mg/ml. So, if you convert the 4 pounds mass into volume it would be: 4 pounds * 453.59 (mg/pounds) *( 1mg/ml) / (236.59 ml/cups)= 7.66 cups.
