Unit of Length

Introduction:

When we try to understand what is the basic unit of length, well, there isn’t a standard unit of length. This is because there are several measurement methods or systems that are currently used around the world. Further, there are several systems that specify their own basic unit.

However, the most common units that are used presently are U.S. customary units and the metric units including SI and non-SI units. Additionally, British Imperial units are also still used in some countries. Let’s look at some of the units in detail.

What is the SI Unit of Length?

In the metric system, the SI unit of length is a metre which is defined as:

“The length of the path travelled by light in a vacuum within 1⁄299792458 seconds.”

Some of the other units also include:

  • kilometres
  • nanometer
  • millimetres
  • centimetres
  • meters
  • decimeters

To get an idea of how big the metric units are, look at the table below

Metric
Example
Millimetre The thickness of a plastic id card or a credit card is about a millimetre thick
Centimetre A fingernail is about a centimetre wide
Meter A guitar is a meter long
Kilometre The distance between cities is measured in kilometres

Other Non-SI Length Units

If you look at the Imperial and U.S. customary systems then the basic unit of length is the yard. Some of the other units include:

  • thou (1⁄1000 of an inch)
  • line (1⁄12 of an inch)
  • inch (25.4 mm)
  • foot (12 inches, 0.3048 m)

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