On the measurement front ....
First, don't convert back and forth - it will drive toy to distraction.
Secondly, the non-metric measurement systems do have some internal logic, it is just that the internal logic doesn't apply system wide. As an example, the 1 ounce - 8 ounces to the cup - 4 cups to the quart - 4 quarts to the gallon progression is useful and practical, just not as rigorous and logical as the equivalent metric progression.
And there is no apparent relationship between units of mass, length and volume.
The non-metric units themselves are in most cases way older than the metric equivalents - they became "standard" over centuries of use, and tend to have originated (haphazardly!) as a result of practical, everyday requirements. For that reason, they tend to have a real-life sense of scale - a liquid ounce is way easier to visualize than a milliliter.
I am blessed/cursed with being of the generation (in Canada) that was educated in both metric and non-metric measurements. And here in Canada we are cursed with having both systems in use side-by-side - meat is sold by the pound in one store (with metric equivalents shown in tiny characters) and by the 100 grams in the next store.
I blame all the US TV we see .