In the U.S., the SI system is used extensively in fields such as science, medicine, electronics, the military, automobile production and repair, and international affairs. The US uses metric in money (100 cents), photography (35 mm film, 50 mm lens), medicine (1 cc of drug), nutrition labels (grams of fat), bottles of soft drink (liter), and volume displacement in engines (liters). In 3 domains, cooking/baking, distance, and temperature, customary units are used more often than metric units. Also, the scientific and medical communities use metric units almost exclusively as does NASA. All Aircraft and Air traffic control use Celsius temperature (only) at all US airports and while in flight. Post-1994 federal law also mandates most packaged consumer goods be labeled in both customary and metric units.

The U.S. has fully adopted the SI unit for time, the second. The U.S. has a national policy to adopt the metric system. All U.S. agencies are required to adopt the metric system.