It used to be that what we called a "45 gallon drum" the Americans called a "55 gallon drum". Same drum.
It was a standard joke here, that American tourists swore that they got more miles per gallon on Canadian gas than they got back home, so they thought we had better gasoline.
There was confusion in the recipe books over the size of an "ounce" or a "cup", can't remember the exact details, but American cook books were off when using Canadian sized cups and spoon sizes. There was also some problem about how big a "tea spoon" is ISTR.
Metric was supposed to save us from all that, but it just added to the confusion. One thing it turned out to mean is that now in Canada we have to buy these tiny little paint cans called "gallon cans" with no apparent saving in price! :(