[mrb]

The conversion techniques you explained, I use them myself (that's why they always ask for my help, I can do it in my head.) But the fact many Americans are unable to do that is, in itself, evidence the imperial system doesn't work that well for them.

> This is definitely the worst example. 0°F is really cold. 100°F is really hot.

This might be a sufficient explanation to give to a 5-year-old, but as soon as you need to do actual work with temperatures, this doesn't work so well. Case in point: many Americans don't know the freezing and boiling point in ⁰F. So, no, it's not "objectively better."

> That's like saying "100 centi 57 meters"

No European ever says this. In contrast, many American routinely say "six pound five".

> How long did they live in the US and how long have they lived where they are now?

Their whole life. Born and raised in America.

[Gormo]

American here. I've never once in my 40 years on this earth heard someone say "six pound five". That parlance is often used for feet and inches (almost always in reference to human height), but I've never encountered anyone using it for pounds and ounces.

[nkurz]

I'm American, have lived in many parts of the US, and I agree: "six pound five" is not something that we say. As Gormo says, this construction is frequent for feet and inches ("six foot five"), but would not be standard for weight.

And personally, if I were to use this nonstandard construction, I'd probably pluralize "pounds". I don't know why "foot" is usually singular in the parallel construction.

The most charitable interpretation I can come up with is that your relatives are from the American South, and are actually saying "six point five", meaning 6 and half pounds, and you are mishearing them.

[sfRattan]

> But the fact many Americans are unable to do that is, in itself, evidence the imperial system doesn't work that well for them.

The set of anecdotes you have put forward about Americans you know could be evidence of any number of things. You hypothesis is that the US customary system doesn't work well for them. An equally valid hypothesis is that public education doesn't work for them.

You keep asserting that your anecdotes are broadly indicative, but multiple people are telling you the opposite (and presenting an equivalent level of anecdotal evidence with similar limits in broad applicability).

For my part, I've lived in several parts of America my entire life and never met another American:

* who says "six pound five" for weight.

* who doesn't know that water freezes at 32°F.

* who would express length/distance as tenths of feet (e.g. 1.3). [1]

But I wouldn't therefore conclude anything about Americans generally.

In fairness, you could probably take a camera and get an 'average man on the street is dumb' effect if you looked hard enough and cut a bunch of disparate interviews together. I suspect you are encountering selection bias. All the people who are bad at math (independent of measuring system or educational background) have found and glommed onto you for help. All the people who don't have trouble with unit conversion (who possibly outnumber the former group) don't trouble you with their unit conversions.

[1]: I have seen halves and quarters (X.25, X.5, X.75) of feet expressed in decimal.