On this day in history, in 1791, the Metric System was proposed for the first time to the Paris Academy of Sciences. The main features of this system were to standardize a set of interrelated base units and prefixes in powers of 10. The system was first developed for commercial use, but the standardized unit size made it particularly suitable for science and engineering.
In the late 1700s, most countries had their own systems of measurement. There was no consistency in the magnitude of units or in the relationships between multiples. The metric system was proposed as a cross-cultural solution. The original plan has mostly succeeded, with only three countries using different systems of measurement as the standard: the United States, Myanmar, and Liberia.
The original metric system defined five units: the mètre for length, the are for area of land (100 square meters), the stère for volume of stacked firewood (1 meter cubed), the litre for volume of liquid, and the gramme for mass. Most of these are no longer in use, as they continued the trend for having a separate base unit for related dimensions (such as the mètre and the are), but the term are became hectare, which is still in use today.
France adopted the original metric system officially in December of 1799. We owe its early spread and usage to Napoleon, as the areas annexed by France at that time inherited the system.
Today even the US uses the SI units for science and mathematics, though imperial units are much more commonplace outside of the STEM fields. Mathematics is the most universal subject- numbers are the same across cultures and borders, and having a unified system of measurements serves only to facilitate communication.
For Americans like us at the Center, check out this XKCD comic about converting to the metric system.