American living in Canada here. It took me a couple of months at most to get used to both. I still couldn’t give you an accurate conversion between metric and imperial, but my brain understands the metric units now. It’s just a matter of using the units in everyday life.

Speed and distance were probably the easiest ones for me. You set your car’s dash to use km/h instead of mph. Then you just follow the road laws like normal. If it says the speed limit is 100 km/h, you just don’t let the number on the dash go much above that. Or you just drive the same speed everyone else does like you do on American roads anyway.

Temperature was a bit more confusing, but you pretty quickly learn that you’ll be happy if you set the thermostat to 18-24 and that if the temperature outside hits 30, it’s going to be a hot day. That kind of precision is more than enough for your mind.

I genuinely used to think I’d have a hard time switching to metric for most things. In my mind, I’d always have to be converting things back to imperial in my head. But that just isn’t the way it works. You quickly just start to relate the units to the real world and you understand it pretty quick.