Strange Planet by Nathan W. Pyle

Logical, mathematically convenient, but not practically convenient. Without a measuring tool, there's no good way to estimate anything besides a centimeter.

Every imperial unit of measure can be estimated whilst naked (but preferably clothed).

An inch is your distal thumb phalanx. A foot is your foot. A mile is, or was at one point, roughly 1,000 paces.

The weather can be estimated by going outside. Is it too hot? It's in the upper third of the 100 degree scale. Too cold? Lower third, might snow. Cool enough to fully dress, but not too cold, right in the middle.

A healthy, big person is about 200 lbs. A very small person is about 100 lbs.

Converting between these units is useful in science, which is why science uses metric. But you could live your entire life on earth and never need to know how many distal phanages are in 1,000 paces. It literally never comes up. Who cares?

It's why units are divided into fractions, rather than into a decimal system.

By the way, the only reason we use a base 10 numbering system in the first place is because we have ten fingers and it was easier for early mathematicians to count. But I digress.

If you're dividing a length of rope, and all you have is the rope, it's simple to divide it in half, and then half again, and then again in half. You could even divide into thirds, if you were feeling frisky. You just fold it over itself until the lengths are even. There are two friendly numbers that are difficult to do that with, though. Can you guess what they are? If you guessed 5 and 10, you nailed it, good job.

Same with piles of grain or hunks of beef or chunks of precious metals.

But what about units of volume, you ask? I don't have a part of my body that holds roughly 8 oz of fluid to pour out. No, for that you'll need a cup. Just a cup. Not a graduated cup with a bunch of little lines down the side. 1 cup. Or half a cup, or a third, or maybe a quarter cup. Again, easily divisible for easy measuring without any special tools.

But a gallon, you protest. A gallon is 16 cups! What the fuck is 16 cups good for? Why not 10 or 100, or create a decigallon for simple math? Because 16 can be divided in half 4 times. Measuring out portions of the whole is as simple as pouring out equal portions into similarly sized containers. Divisible numbers are easier to use without graduated equipment.

And that's why time is measured in 24 hours, each hour is 60 minutes, each minute is 60 seconds. There's a ton of history there, and we'll ignore for this discussion the inaccuracy of measuring a day or a year. If the metric system is entirely superior, why don't you demand we all switch to metric time? A year will still be roughly 365 days (again, setting aside the inaccuracy) but we could divide the day into 10 equal metric hours, or mours, and those mours into 100 metric minutes, or metrinutes, and then those metrinutes into 100 metric seconds, or meconds. 1 mecond would be 0.864 seconds, and a metrinute would be 1.44 minutes, which to most people would be an imperceptible difference in time. Hey, how many seconds is 1.44 minutes? You don't know without a calculator because we don't use metric for time, and it probably never bothered you once before now. What an insane, non-logical unit of measure time is.

Yes, metric let's us convert millimeters to kilometers, or helps us determine how many calories it take increase 1 cubic centimeter of water by 10 degrees kelvin. It helps with those things because the units are arbitrarily defined to make the math easier, not to make the measurement easier. But that's it, there's no additional sanity, no additional logic. It's easier to convert between units via math, because it was designed to be easier to convert between units via math. There are no additional benefits to the metric system.