Here's one for the weekend.
Units of length
"The system for measuring length in the United States customary system is based on the inch, foot, yard, and mile, which are the only four customary length measurements in everyday use", according to Wikipedia. And I do know that the UK and the US have some sort of an agreement on these units (with exceptions).
I have a question, which may seem odd at first glance, but there is a reason for asking. I'm writing, amongst others, a software routine that converts between units of length. I also know there is probably not a definitive answer, so I'm looking for feedback based on everyday normal use. This is not a trick question, so all answers will be considered in my final evaluation, and encoding.
Now, with that out of the way, here is the question.
When do you, in everyday use, switch from inches to feet, and when from feet to yards, and when from yards to miles?
I know that 12 inches equals 1 foot, and 3 feet equals 1 yard, but do you usually say e.g. something is 36 inches or 3 feet, or one yard, long or distant? Or are inches used to avoid fractional feet ('x' feet and 'y' inches)? Or is it context dependent, e.g. when talking about precise measurements you use the smaller unit of length? Or are you not an engineer and convert everything to the largest practical unit, 'x' feet and a bit (but then when does the bit become large enough to give it more meaning, like 'give or take an inch')?
The same for yards and miles, but maybe the same principles apply?.
Thanks in advance for some soul-searching (or maybe there is an official recommendation?) and any resulting useful feedback you may have to offer.