No idea. I had to learn it when I was in elementary school because all of the teachers were convinced that we’d be switching in the near future. All these years later we still haven’t switched. The odd thing is, the change could be made fairly smoothly. First, you make it a standard part of education (which it should be anyway). Second, the US makes it a policy to replace all worn out road signs with signs showing both metric and US customary units (with the metric units being more prominent).
This is money that will be spent anyway, so we might as well use it to help the transition. Assuming the first step has already been put into place, there can also be a provision for this to stop after a period of time so that all replacement signs after the specified date are metric only. If everyone by that point has been educated in the metric system and has been made aware of the imminent switch, there is really no need to be sympathetic to anyone who simply refused to learn.
The same strategy of education and attrition should work to minimize the costs in other sectors as well. Introducing the change through signage, however, has the advantage of letting people get used to the new system while still having the old one there to help them just in case. Not many machines can be replaced with dual-system versions, but the dual-system signs could help people get used to it and not feel so put upon by the transition (thus addressing the fear of change mentioned a few times above).
@downtide It seems to me that 41 years is a rather short period of time in the grand scheme of things. One generation has only been taught metric measures at present, but what do you think things will be like a few generations on when everyone will have grown up learning only metric?
@CWOTUS @marinelife I’d be curious to see numbers regarding the conversion costs and what kind of transition schedule those numbers are assuming. An overnight transition would certainly be very costly; but then again, we already know that not converting has cost the US large sums of money (such as the $328 million lost all at once when the Mars Climate Orbiter was lost).