The metric system standardized weights and measures enabling trade and improving communication. Before the metric system, every country and also countless regions, used different forms of measurement. This vastly complicated international trade.
The metric system derives from the natural world and uses a decimal counting system for simplicity.
Length derives from the meter, a measure of one ten-millionth the distance from the North Pole to the equator. One thousand meters is a kilometer, kilo being Greek for thousand. A centimeter is 1/100th of a meter. A landmass 100 meters squared is a hectare.
Volume derives from length: a liter is the volume of water that fills a container 10 centimeters cubed.
Weight derives from volume. A kilogram is the weight of one liter and a gram is 1/100 a kilogram.
Like countless countries that came later, the French initially resisted the metric system. It wasn’t until the mid-1800s that the metric system became widely used in France. The system spread to other countries based on its simplicity and objectivity. For example, there was no need to adopt the length of a foreign king’s foot as a unit of measure.
Only three countries in the world have failed to adopt the metric system, Burma, Liberia, and the United States. Metric is the official system in the UK but, thanks largely to the US refusal to switch, many British change between metric and imperial measurements.
Metric in the US
The United States officially adopted the metric system in 1866 but, except for the limited use of liters, Americans largely refuse to use metric. Even liters are still confined largely to soft drinks but larger measurements of fluid are referred to in gallons.
If Americans realized how much simpler metric is they’d surely switch. Since most liquids weigh about the same as water it is easy to measure liquid, say for recipes, by weight. Kilometers are shorter than miles but, as anybody who has driven in Europe knows, they are easy to estimate. American runners routinely run “5K” (five kilometers) and don’t complain about using the metric system. There is no need to remember arbitrary measurements; the number of quarts in a gallon or cups in a quart.
The US last attempted to change to metric in 1975. However, the move failed. Many argue the change was too fast. All signage, weights, and measures changed seemingly overnight to an unfamiliar system.
One notable failure based on a refusal to convert is the crash of the Mars Climate Orbiter, a 1998 spaceship. One group worked in metric and another using the imperial system. Due to a mismatch between metric and imperial, the ship flew too close to the planet and crashed.