NOTE

This document expects a very basic understanding of multiplication and division.

Standards for Distance

The concept of measuring distance is a very important human invention. In the past, people used to measure distance by using their feet, hands, or other body parts: this was useful because it allowed people to tell each other how far away something was without having to use any tools. However, this method was not very accurate, and it was difficult to compare distances between different people.

Today, we have a standard system of measuring distance that is used all over the world. This system is called the metric system.

NOTE

Some countries, such as the United States, still use a different system of measuring distance called the imperial system. However, the metric system is more widely used and is considered to be more accurate and easier to use.

The Meter

The basic unit of distance in the metric system is the meter. The meter is defined as the distance that special particles, called photons, travel in exactly 0.00000000333564095 seconds (this is not a random number, it was chosen for a specific reason). This definition is very precise and allows us to measure distances with great accuracy.

A meter is approximately equal to the length of a baseball bat, or the width of a door. It is a very convenient unit of measurement because it is easy to visualize and compare to other objects.

This cube is one meter on each side.

History of the Meter

The meter was originally defined in the year 1799, around the time of the French Revolution. The French government wanted to create a new system of measurement that was based on the natural world, rather than on human body parts. They decided to define the meter as one ten-millionth of the distance from the North Pole to the Equator, measured along a line that passed through Paris.

This definition was very precise, but it was difficult to measure accurately. In 1983, the meter was redefined in terms of the speed of light, which is a constant and can be measured very accurately. This new definition is the one that is still used today.

Diagram of the original definition of the meter. A "km" is one thousand meters.

Metric Prefixes

Please refer to the Standards for Metric Prefixes document for more information.

Other Units

Other units than the meter are used to measure distance in some places, such as the mile or the foot. They are generally considered to be outdated and are not used in scientific or technical contexts.

Approximate (not exact) conversions:

• 1 mile is approximately equal to 1.6 kilometers.
• 1 foot is approximately equal to 0.3 meters.
• 1 inch is approximately equal to 2.5 centimeters.
• 1 yard is approximately equal to 0.9 meters.
• 1 nautical mile is approximately equal to 1.8 kilometers.
• 1 furlong is approximately equal to 200 meters.

More units exist. You may find it useful to research these units if you are interested in learning more.