Everything that matters to people is as easily mapped out to metric units. I know how to span my fingers to get either 10 cm, 20 cm or 25 cm, and how to pace my

Everything that matters to people is as easily mapped out to metric units. I know how to span my fingers to get either 10 cm, 20 cm or 25 cm, and how to pace my steps to get 1 m. Arm span is easy too, I simply get my height and can work based on that, as I do when measuring heights. Step pacing is quite visible and I see it regularly in the open in various contexts. Metric people know how to do these kinds of things. Real estate agents or construction workers might refine their paces to achieve greater precision, but even people who have never had the curiosity or need to do so can get a rough estimate of a meter that's probably good enough and not much more imprecise than the length of the step of another person (like feet… Charlemagne's giant foot became the standard unit for peasants with half the foot size for centuries…). I've never felt any personal interest in measuring weights based on fist-sized rocks either (sandstone or granite by the way? you've got all sorts of density ranges out there…), but I'm sure you could find something as intuitive if you needed it and I sure can get of sense of weights expressed in grams in a kitchen and have also developed a pretty good intuitive feel of heavier stuff based on a few experiences moving 25 kg and 50 kg bags around that proves useful from time to time.