They don’t understand the metric system.
There are only three countries in the entire world that don’t use the metric system and the United States is one of them. Instead of meters, kilometers, and liters, for instance, Americans use things called inches, feet, miles, and gallons that have little to no consistent relation to one another. And instead of the Celsius temperature scale, Americans use a system of measuring temperature called Fahrenheit which flat-out just doesn’t make any sense.
Despite the fact that Americans have their own weird way of measuring things, they also have no idea how to use the metric system when venturing out into the rest of the world.