I used both in my career and was fine with either
Ditto, but how much does a gallon of water weigh, and how many cubic inches in a gallon?
In SI (metric), it's easy to remember a liter of water has a mass of 1 kilogram, and a liter contains 1000 cubic centimeters. I think in terms of feet, pounds, and gallons, but I often check unit conversions with SI measures.
