[QuercusMax]

In practice these are just big numbers you memorize. 5280 feet in a mile, 63360 inches in a mile, 1760 yards in a mile...

It's not like you often have to do math with them, outside of school math problems. A year isn't precisely 365 days, and months are all different lengths. It's just more of the same type of thing; doesn't actually cause problems when distances are usually expressed in miles anyway.

[remram]

From polling my American friends, ask them how many yards in a mile and they'll answer 5280. They don't really know how the system work and can only vaguely remember (one of) these numbers.

The system is not meant for units to be converted.