I own two pairs of men's boots, from different companies, with US sizes on the label 2.5 apart from each other. They're the same physical size, and both fit me

I own two pairs of men's boots, from different companies, with US sizes on the label 2.5 apart from each other. They're the same physical size, and both fit me perfectly. That's pretty typical. I generally have to try new shoes in about a 3-size range. According to the L x 3 - 24 rule, these boot should be nearly an inch different (or at least, their lasts). Maybe the US system is theoretically simple, but in practice it seems to be just an arbitrary number that can't be meaningfully compared to anything except the same model of shoe from the same company. In contrast, I've ordered shoes from Japan 3 times, from 3 different companies, and I did it by putting a ruler next to my foot, and then choosing that number of centimeters in the online form. Every time, I got a shoe that fits great. Maybe using an absolute length doesn't solve all problems, but my experience (with sample size of probably N<20) is that it works far better in practice. An arbitrary unit of measurement removes accountability, by way of obfuscation, and gains us nothing.