You've really opened a can of worms here! <---Idiom.
The United States still clings to the "U.S. Customary" system. The metric system--properly called "the International System" or "SI" (Systeme Internationale) is universally used in science and in medicine. In other technical fields, such as engineering, it varies. My son is a mechanical engineer who designs HVAC system and they still use feet, gallons, and BTUs (British Thermal Units). There are weird things: I worked at a company that designed high-tech gear and all of the blueprints used the metric system--but ALL of the actual distances and sizes happened to be values like 25.4 mm, 50.8 mm, etc!
In ordinary daily life we use the U.S. Customary system. Weather reports give temperatures in degrees Fahrenheit. I always have to make conversions when talking to my language partners. When I add air to my tires, I read the pressure in PSI (pounds per square inch).
During the 1970s there was a push for metrification, and it was widely expected that the United States would be converting to the metric system. For a while, road signs on the Interstate highways gave distances in both miles and kilometers. Kitchen measuring cups for a long time have shown graduations in both systems, but I own one I bought during the 1970s that has milliliters on the front where they are easy to read, with fluid ounces and cups on the back. Actually you can see a picture of that cup on Wikipedia--I added it to the article on "Metrification in the United States." When cooking, our recipes show quantities in teaspoons, tablespoons, fluid ounces, cups, pints, and quarts.
Under President Reagan, the U.S. abandoned the plan to "go metric" and I don't there are any plans now. This leaves the United States, Myanmar, and Liberia as the only three countries that are not officially on the metric system.