A Brief History of the Metric System
How the metric system was created during the French Revolution, how the definition of the meter evolved from a physical bar to a fixed physical constant, and how metric units became the global standard.
Published
The metric system was created in France in the 1790s, during the French Revolution, as a deliberate replacement for the patchwork of regional measurement units that had made trade and science needlessly complicated. Its core idea — that units of measurement should scale in powers of ten and be based on reproducible physical constants rather than royal decree or local custom — is why it became the basis for the modern International System of Units (SI).
A revolutionary measurement system
Before the metric system, France alone used hundreds of different local units for length, weight, and volume, many varying from town to town. The French Academy of Sciences was commissioned to design a unified, rational system based on nature rather than arbitrary reference points. The result, adopted in the 1790s, defined the meter as one ten-millionth of the distance from the North Pole to the equator, measured along a meridian passing through Paris.
From a physical bar to a physical constant
For most of the metric system's history, the meter was defined by physical reference objects: first a platinum bar, later a platinum-iridium bar kept near Paris. In 1960, the meter was redefined in terms of the wavelength of light emitted by krypton-86. Since 1983, it has been defined as the distance light travels in a vacuum in 1/299,792,458 of a second — a definition based on a universal physical constant rather than any physical artifact that could be damaged, lost, or drift slightly over time.
Global adoption
The metric system spread gradually through the 19th and 20th centuries, adopted first across much of continental Europe and eventually by nearly every country in the world for official use. The International System of Units (SI), formalized in 1960, standardized the metric system's modern base units and is now the world's dominant measurement system, with the United States as the most prominent holdout for everyday, non-scientific use.
Frequently asked questions
- Who created the metric system?
- The metric system was developed by French scientists during the French Revolution in the 1790s, commissioned by the French Academy of Sciences to create a rational, decimal-based system of measurement to replace the patchwork of local units used across France.
- What is a meter defined as today?
- Since 1983, the meter has been defined as the distance light travels in a vacuum in 1/299,792,458 of a second — a physical constant, rather than a physical artifact like the original platinum bar kept in France.
- Which countries don't use the metric system?
- The United States is the largest economy that has not fully adopted the metric system for everyday use, though it is used in science, medicine, and much of manufacturing. Most other countries have adopted metric units as their official system, even where some imperial units persist in casual use, such as pints in UK pubs.
- Why was a decimal-based system considered an improvement?
- Before the metric system, units varied by region and often used irregular ratios (12 inches to a foot, 3 feet to a yard, and so on), making conversions and trade calculations cumbersome. A system based on powers of ten made calculations, science, and international trade far simpler.