Not that many years ago, at least in Arkansas, you could be arrested for possession of a kitchen scale that gave weights in grams. Drug paraphernalia, dontcha know. Somebody could weigh some reefer on it!!!
For old guys like my friends (I will not say "and me") the conversion for speeds is mostly complete. That's because speedometers and speed signs converted totally. It's not exactly complete for us (actually for anyone) since the fools to our south are unable to handle the change so acceleration times in car mags and such are in seconds to 60 mph (with an admixture of seconds to 62 mph).
The handy part of that conversion is that many cars have both scales on their speedometers; my Honda Accord in the USA does. Though from what I remember on Continental Europe is that they only had kph and I recall that when I asked about this here a year or two ago it turned out that British cars will have both scales. Don't know how it is in Canada but I would assume dual scale.
Doing renovations back in the 80's I got slightly messed up by the conversion. Out 2x4's (and others) went metric in those dimensions. But they are cut extremely close to the metric size for 2 and 4 inches (which, of course they are not, more like 1.5 x 3.5 dry). But they are not exactly so when in the middle of a reno you mix old and new they don't line up precisely. That problem went away quickly enough.
From a Canadian video on the matter, he said that construction sizes (eg, plumbing) are in inches. But even without going metric, that problem with 2×4's already existed in the USA in the 60's. The actual dimensions had been reduced to 1-7/16 × 3-1/2, while the original 2×4's in an old house's walls actually measured as 2×4. When we closed off a doorway in one remodel, we had to rip half-inch thick furring to build the wall out.
Temperature was converted in the 70's and I'd say everyone is on Celsius for that. At this point I find F temperatures difficult even though I grew up with them. I know immediately how warn or cool or hot or col C is but have to make a rough conversion of a F temp to get a feel for it. That is other than around 100 F. That one I just know is hot.
That was my first concentrated research into devising an easy conversion method. My friend and I were going to Europe for her first time and she was worried about knowing the temperature, so I worked one out for her. An illustration of her problem was offered by an American ex-pat living in Germany in which she's dressed for winter and asks if she's dressed appropriately since it's forty degrees outside.
First I started with a single memorized mid-scale value: 20°C = 68°F. Then going up or down from there by 5 degrees C is the same as 9 degrees F while for 10 degrees C it's 18 degrees F. And going up or down by a single degree C then figuring 2 degrees F is close enough (9/5). That is, start from a known point and work your way up or down. There are a number of videos from India that do the entire conversion formulae but in a simplified form using a factor of 2 (instead of 9/5) and an offset of 30 (instead of 32).
I finally settled on identifying temperature ranges of cold, cool, comfortable, warm, and hot, based around 20°C as the lower end of the comfort zone. Go lower and it gets increasingly colder; 10°C (50°F) is getting into winter temperatures. Go higher and it gets increasingly warmer -- at 30°C (86°F) it's getting hot. At 40°C (104°F) it is most definitely hot.
So to decide how to dress when you go outside, you mainly just look to see how far from 20°C you are. Which seems a lot easier to work with than the much wider ranges of temperatures in Fahrenheit.