1976

It was a process that began in 1970. It took 11 years to finalize the process when gas finally became a metric unit.

I remember Canada switching over to all this when I was in about grade 3 or so, so around 1980 or so it must be. I started learning imperial and then switched to metric so ironically instead of learning both I ended up learning neither. I still don`t understand pounds from kilograms or miles to kilometres. What a mess.