# How Long Is a Meter? How Is a Meter Defined?

From determining how far you have to drive to get to a destination, to guessing how long something is, measurements play an important role in our daily lives. And among the most important of such units of measure is the meter, the base unit of length in many metric systems, including the International System of Units (SI units).

While use of the meter is common today, that wasn’t always the case. Our modern measurements had to be invented somewhere. And often, these units of measurement have evolved over time. The definition of a meter, for example, has changed throughout history. So just how long is a meter? And how is a meter defined? Let’s take a look.

## The History of the Meter

In approximately 888, after the fall of the Carolingian Empire, the standard measures of length throughout Europe differed from one another. Within certain jurisdictions, measurements could be standardized, but jurisdictions were sometimes nothing more than a small market town. Within larger regions, units of measure varied widely.

More often than not, units of measure at this time were used to determine taxes (a piece of cloth, for example, would be taxed based on its length). Many measurement units were dependent on who was ruling at the time, and they could change on a whim.

After the French Revolution began in 1789, and with Enlightenment ideals still popular, a greater emphasis was placed on standardizing units of measurement within the scientific community. In 1793, the French National Convention adopted the proposal from the French Academy of Sciences. The Academy had advised the adoption of the mètre (“measure”), a basic unit of length that could be defined scientifically.

At first, there was resistance to the change, but the meter was adopted in America and continental Europe in the mid-19th century. In 1875 at the Metre Convention, the meter became the official international measurement unit.

Trying to standardize a measurement worldwide wasn’t without its difficulty. The goal was to ensure that standard measuring bars were available to every country in the world, but it was impossible to know if the bars were the right length because no one knew for sure whether or not the countries were working with standard and correct measurements.

Something needed to change to make the unit of measurement consistent throughout the world. As science usually does, it set out to improve upon its previous work and find ways to make life easier and put everyone on the same page when it came to the meter.

## How Long Is a Meter and How Is a Meter Defined?

In the 1790s, the French defined the meter as one ten-millionth of the distance from the North Pole to the equator as it passed along a meridian to Paris. This actual measurement is represented on an iron bar that is housed in Paris.

In 1927, the definition of the meter was updated and defined more precisely. For this definition, the meter is the distance from 0 degrees, between the axes of two central lines that are marked on a bar of platinum-iridium. The bar is subjected to standard atmospheric pressure and held on two cylinders, which are at least one centimeter in diameter, and are placed on the same horizontal plane exactly 571 mm from each other.

In 1960, the definition of a meter was changed again. This definition was based on the wavelength of krypton-86 radiation. In 1983, the definition was once again changed to define a meter as “the length of the path traveled by light in vacuum during a time interval of 1/299,792,458 of a second.” This is the definition of a meter we use today.

Finding a standardized, universal unit of measurement was required by science, and they set out to find a way to develop this unit so that it could be applied worldwide. While there was some trial and error, they eventually came up with a unit that has been adopted and used by countries everywhere. Who would have ever thought the meter would have such a complicated and interesting history?