An inch it about the distance between the two knuckles on your forefinger.
A mile is about one thousand steps, or fifteen minutes of travel at a brisk pace
A cup is a cup, before portion sizes got daffy there was a pretty common cup that everybody had.
“Standard” measurements were refined over thousands of years by actual artisans making actual crafts. Metric was designed by a bunch of rich French people and foisted on the rest of the world because it makes more sense on paper, regardless of how in practical use it requires you to break out a ton of awkward decimals and other contrivances to make it match the human experience.