American public schools have been using metric for decades. Science classes in American public schools use metric exclusively since the 80s at least. When you meet an American who makes a big deal out of not knowing what a meter is, 9 times out of 10 they're putting on a performative patriotic display mean to get a rise out of you. That, or they're quite elderly.

Incidentally, .22 LR is nominally but not actually 0.22 inches in diameter. It's very slightly bigger than that. In the domain of ammunition, there is often a mismatch between actual diameter and nominal diameter.