One may notice the OP's dimensions do not match any "standard" dimensions. The 14in height, rather than the 16in, would make that difference. I was just guessing when I said "marketed at 20g". For all I know it may have been marketed at 18, or even 17.5, but both those are wrong as well. Reporting a 17.45 gallon tank is a bit much. (Just like marketing a 41.47inch tv would be). <-Made that number up. What's also interesting is that our forum's calculator reports 17 gallons, when the actual volume is 17.45g. Hmm.
The thing that is the same with both of our nations is that they both have superiority complexes, as a state and many individuals. (I'm not saying you do, I just notice that a lot when Brits and 'Mericans start arguing.)
Just to ask, how are your computer screens and tvs marketed for size? How big is the petrol tank in your car? Speaking of cars, how many miles per gallon or liters per 100 kilometers do you actually get? How long does your laptop battery last? I'll bet manufacturers get away with more than you suppose. (Yes those last two are conditions of many things, not just straight measurements.)
Well, such are the inadequacies of the Imperial System of Measurement (and the US Customary Units): some of the time (much of the time), they just are inconvenient. I love BTUs though. Sigh, can't we just switch to SI? (No, the US has tried lots of times
http/en.wikipedia.org/wiki/Metrication_in_the_United_States).