It's all metric behind the scenes. When you pump your gas it shows gallons, but it's doing the math in litres. We turned our backs on the ⅓ lb burger, we've trained corporations to treat us like idiots.
Every food label, with very few exceptions, lists the contents in either grams or milliliters, in addition to ounces or fluid ounces. Every thermometer I've ever seen has both Fahrenheit and Celsius scales. We buy electricity in watts with metric currency. We measure the light output in lumens, and the common lightbulb sizes are measured in millimeters, but the wires that carry the electricity are measured by AWG. The parts on my bicycle and car all use metric measurements, except for tires. Tires are an unholy abomination with section width given in millimeters, the cross-section in a unitless ratio, and the rim diameter given in inches.
Meh, what're you gonna do? We switched to, or adopted, SI and metric where it made sense, but we have a lot of legacy systems.
The units Americans use (Miles, feet, cups, ounces, etc.) actually are Metric units. They're just not the standard ones. Because, again, The United States has been on the Metric system since the late 1800s like every other Western country.
The majority of U.S. customary units were redefined in terms of the meter and kilogram with the Mendenhall Order of 1893 and, in practice, for many years before
Not redefined as 'metric'. It means the base measurement is connected to SI along a fixed constant. Meters and kilograms are the base units for length and mass in SI, which is actually metric. The respective USCU units for length are inch, foot, yard, and mile and mass a really annoying number of things.
The systems of measurement are connected, but USCU is not metric.