People stop asking me to convert to Imperial pretty quick.
It took me an embarrassingly long amount of time to realize that there are four quarts in a gallon...
I have no such trouble with any SI unit. So with that, I will leave you with this!
"For of all sad words of tongue or pen, the saddest are these: 'The French were right again!'"
They were drilled into my brain when I was in primary school: 10, 100 and 1000.
[0] well, really, it uses metric with a redefined version of the old US customary system layered over it to prevent people from noticing, but...
Now, choosing wine gallons as our standard gallon, that might deserve a little blame.
In Sweden, 1 foot was around 28.96cm (in modern dimensions), whilst 1 foot in Amsterdam was 28.31cm.
On such differences (OK, and a few other contributing factors) a ship was sunk.
Imperial height is because 6 feet is the generic height of a "tall person" - we get so much of our sporting news from overseas and no one bothers to convert it.
5 us gallons is about 4 imperial gallons.
In practice the volume units are a much bigger problem. I have not hit anyone with the "cubic hand" yet...
Also, the US doesn't use imperial, dammit. It uses US customary units. They're related but different systems with radically different definitions on many units.