Myanmar, Liberia, and the United States of America. Those are the only three countries left in the world that don’t use the metric system. Ted-Ed traces the history of the metric system (thank you French Revolution) to show how important it is to have one universal measurement system for the world, what can happen when conversions go wrong (NASA crashing an orbiter into Mars), and what the future of the metric system will be (basing it off universal constants like the speed of light).

Source: Why the Metric System Is So Important