How many cups are in a gallon?
1 US gallon = 16 US Cups (exact) = 15.14 Metric cups
1 Imperial Gallon = 19.215 US cups = 18.18 Metric cups
I would agree totally on your US measurement, but in the rest of the world, a 'cup' is a nebulous amount and I think depends on which country you are in.
In UK, a cup is half of an Imperial pint. I cannot find a 'metric cup' defined anywhere with authority, and your amounts specified above make it exactly half a litre - (that's a very large cup). This entire issue is further complicated by the usage of 'liquid'cups and 'dry volume' cups, and the use of ISU or SI (International System of Units) in some countries instead of 'original'Metric.
A very confusing issue indeed!
1 gal = 16 cups
1 cup = 0.06 gal
1 gallon = 16 cups
1 cup =0.23 gallon