The Global Standard: Metric (SI)

The metric system, born from the French Revolution, is based on powers of 10. It is the language of science and is used by 95% of the world.

• Pros: Easy conversion (1km = 1000m), consistent prefixes (Kilo, Centi, Milli).
• Cons: None, really. It's logically superior.

The Holdouts: Imperial / US Customary

Used primarily by the USA, Liberia, and Myanmar. It evolved from ancient Roman and Anglo-Saxon units.

• Pros: "Human-scale" units (a foot is roughly a foot length). Fahrenheit is often argued to be better for weather (0-100 scale fits human habitability).
• Cons: Converting is a nightmare (12 inches = 1 foot, 5280 feet = 1 mile).

Fun Fact: The Mars Climate Orbiter

In 1999, NASA lost a $125 million Mars orbiter because one team used metric units (Newtons) and another used Imperial (pound-force). Oops.