And...to add to the confusion....One Calorie is the amount of heat energy needed to raise one kilogram (or one liter) of water by one degree Celsius. The Metric system is far more unified. Volume, weight and linear measures are all designed to work together. So a kilo of water should be exactly one liter, and a liter is 1000 cubic centimeters--10x10x10cm.

But I won't try the conversions of pool volume....

BTW, the Rule of Thumb method of chlorine calculation works just as well if you substitute liters for gallons.