Length Converter

Updated on by Stefan Banse

Units of length were initially developed on a historical basis and varied from country to country as well as in the various fields. For example, in the craft trades, there were always various other commonly used measuring units.

Since then, the metric system using the meter as the basic unit of length in the international unit system SI (System international unites) has been specified as the standard unit of length. However, other units that are not part of the metric system are also in use. The units of length used in Anglo-American countries, such as mile (mile), yard (step), foot (foot) and inch (inch). In astronomy, we use units as light-years, astronomical units or parsecs. And in aviation and seafaring, nautical units of measurement are used to measure the miles or the fathom.

All these length units can be easily converted or converted into other units by using the following length converter.

User Guide

Enter the length to be converted and choose the unit of length from and to which you want it to be converted. The length converter provides standard metrics, Anglo-American, nautical and astronomical measures of length are commonly used for calculation. Additional information on different length units can be found by clicking on the question mark symbol on the calculator.

Metric units of length

The metric system is the unit system using the meter as the basic unit to measure total distance. Unlike other unit systems, decimal multiplications or decimal fractions can easily be calculated here. Below are some of the length units:

Kilometer (km)

The unit kilometer belongs to the metric system and is derived from the basic unit meter. Here, 1 kilometer can be converted into 1,000 meters or 1 meter is equivalent to 0.001 kilometers. The kilometer belongs to the International System of Units (SI).

Meter (m)

Meter is a basic unit of length in the International System of Units (SI) and other metric systems. Since 1983, the meter has been defined as the distance travelled by light in 1/299,792,458 seconds in a vacuum. All other units of length in the metric system are derived from the meter (e.g. 1 km = 1.000 m, 1m = 1.000 mm).

Decimeter (dm)

The unit decimeter is derived from the basic unit meter. Here, 1 decimeter is converted to 0.1 meters or 1 meter is converted to 10 decimeters. The decimeter belongs to the International System of Units (SI).

Centimeter (cm)

The unit centimeter is also derived from the basic unit meter. Here, 1 centimeter is converted to 0.01 meters or 1 meter is converted to 100 centimeters. Like the meter, the centimeter also belongs to the International System of Units (SI).

Millimeter (mm)

The unit millimeter is also derived from the basic unit meter. Here, 1 millimeter is converted to 0.001 meters or 1 meter is converted to 1000 millimeters. Again, the millimeter belongs to the International System of Units (SI).

Micrometer (μm)

The unit micrometer is also derived from the basic unit meter. Here, 1 micrometer is converted to 0.000001 meters, or 1 meter is converted to 1,000,000 micrometers.

Nanometer (nm)

The unit nanometer is also derived from the basic unit meter. Here, 1 nanometer is converted to 0.00000000001 meters, or 1 meter is converted to 1,000,000,000 nanometers.

Ångstrom (Å)

The unit Ångstrom belongs to the metric system and is derived from the basic unit meter. Here, 1 Ångstrom is converted to 0.0000000001 meters or 1 meter is converted to 10.000.000.000 Ångstrom. This unit does not belong to the International System of Units (SI), but it is used in practical fields such as chemistry or crystallography. For example, Å is the standard scale of atomic radii.

Other metric units

There are many other units of length in SI, which represents multiples or fractions of a meter. For this purpose, unit prefixes are used. In other words, prefixes for the meter, as shown in the previous examples. An overview is given in the following table:

Symbol Name Value
Short scaleLong scaleUnit
Yg Yottameter 1024 septillion quadrillion meters
Zg Zettameter 1021 sextillion trilliard meters
Eg Exameter 1018 quintillion trillion meters
Pg Petameter 1015 quadrillion billiard meters
Tg Terameter 1012 trillion billion meters
Gg Gigameter 109 billion milliard meters
Mg Megameter 106 million meters
kg Kilometer 103 thousand meters
hg Hectometer 102 hundred meters
dag Decameter 101 ten meters
g Meter 100 one meter
dg Decimeter 10-1 tenth of a meter
cg Centimeter 10-2 hundredth of a meter
mg Millimeter 10-3 thousandth of a meter
µg Micrometer 10-6 millionth of a meter
ng Nanometer 10-9 billionth milliardth of a meter
pg Picometer 10-12 trillionth billionth of a meter
fg Femtometer 10-15 quadrillionth billiardth of a meter
ag Attometer 10-18 quintillionth trillionth of a meter
zg Zeptometer 10-21 sextillionth trilliardth of a meter
yg Yoctometer 10-24 septillionth quadrillionth of a meter

Anglo-American units of length

The Anglo-American units of length originated in medieval England. Most of them are measured using our own body, such as foot, hand and ulna. As time passed, they were unified to a large extent and the metric system was eventually adopted as the benchmark for most Anglo-American units of length. However, they do not belong to the International System of Units and do not comply with the SI.

Mile (mi)

The term Mile originated during the Roman Empire as a sequence of 1,000 double steps, or mille passus (thousand steps). Nowadays a distinction is made between the land mile described here and the sea mile described in nautical studies. Therefore, 1 mile is converted to 1.609344 kilometers or 1 kilometer is converted to 0.62137 miles.

Yard/Step (yd)

The length of yard or step is officially approved in Anglo-American countries and is used to describe medium lengths. Over the years, various definitions have been given, for example, the yard was defined as the length of three feet or the distance from the tip of the nose to the tip of the thumb of Heinrich I's outstretched arm. Since 1956, the yard or step has been defined as follows: 1 yard is the converted to 3 feet, or equivalent to 0.9144 meters.

Foot/Feet (ft)

The foot was popular as a measure of length from very early times and it is still in use in Anglo-American countries today. In different countries, its length usually corresponded to 28-32cm. Nowadays only the English foot is used. Therefore, 1 foot is converted to 30.48 centimeters or 1 foot is converted to 12 inches/inch.

Inch (in)

According to history, the inch was first defined by law as 1/12 of a foot, then later as the length of three barley grains strung together. Similar to foot, yard and mile, it is also one of the length units that are not part of the International System of Units, but used widely and approved in the Anglo-American area. Nowadays, inch is fixed to 1/12 of a foot. Therefore, 1 inch can be converted to 2.54 centimeters or 1 centimeter is converted to 0.3937 inches.

Other Anglo-American units of length

After the unification of length units to the metric system in 1959, some length units were retained to keep the existing dimensions of land and property unchanged. These units of length have been used for this purpose only and known as US survey length units. For example, the link (chain link) is converted to 0.2011684 m, another unit for the foot is 0.3048006 m, and the chain is 20.11684 m or the furlong is converted to 201.1684 m.

Nautical length units

Some other measurement units are traditionally used in maritime and aviation. Some of them are:

Sea mile/Nautical mile (sm)

The sea mile or nautical mile is a unit of length frequently used in shipping and aviation. It was originally intended to measure 1/60 degree of latitude. Later, the nautical mile was defined accurately as 1,852.0 m.

Fathom/thread (fth)

The fathom or thread is defined as the distance between the outstretched arms of an adult male and was defined as 6 feet (1.8288 meters). 1 fathom is equal to 1.8288 meters. This unit of length is often used in navigation to indicate depth.

Astronomical Length Units

These units of length are used to deal with the other scales in astronomy. Even though they are not part of the International System of Units, they are indispensable for the distance calculation in astronomy.

Light year (Ly)

A light-year refers to the distance of light (in a vacuum) within one year. There are different definitions for a year (Gregorian year, tropical year, Julian year etc.), therefore the Julian year (365.25 days) was used as a definition for the light year. A light-year is converted to 9,460,730,472,580.8 km, around 9.5 trillion km. For example, the Milky Way is 100,000 light-years long.

Light minute (Lm)

One light minute is defined as the light (in a vacuum) travelled in one minute. One minute of light is converted to 17,987,547.48 km, around 18,000,000 km. For example, the average distance between the sun and the earth is about 8.3 light minutes.

Light second (Ls)

One light-second is defined as the light (in a vacuum) travelled in one second. One light-second is converted to 299,792.458 km, around 300,000 km. For example, the average distance between the earth and the moon is around 1.3 light seconds.

Parsec (pc)

The parsec is an astronomical unit of length and is equivalent to around 3.26 light-years. It is a very powerful tool used to determine the distance between stars because the angles between the stars are very important. A star seems to move a little bit back and forth during the year viewed from Earth. This is because the earth moves around the sun in an interval of 6 months, once relatively to the left and right sides of the sun. The final phases of this star's movements form an angle seen from the earth. This angle becomes smaller and smaller as the star moves further away. The average distance between the earth and the sun is known, so trigonometric results show that an imaginary celestial object, that moves back and forth by a 3600th degree, around 3.26 light-years away from the earth. This distance is defined as a parsec. The back and forth movement are called a parallax movement. A 3600th of a degree is called an arc second. The term parsec is derived from these two terms. This definition makes it very easy to describe astronomical distances, as they are directly derived from the reciprocal of the parallax angle. For example, if the angle is one arc second, the distance is 1pc, if the angle is 0.5 arc seconds, the distance is 2pc.

The astronomical unit (AU)

The astronomical unit is a unit of length in astronomy. By definition, the AU is 149,597,870,700 meters long, which is almost the average distance between the Earth and Sun. Apart from the light-year and the parsec, the astronomical unit is one of the most important astronomical units of length. AU has been very important in history because most measurements were performed using AU and not meters. In 2012, the conversion between astronomical units and meters is precisely calculated and

AU is no longer an advantage. However, the distance in the Solar System is still often specified in AU because of its more practical values.

Source information

As source for the information in the "Units of length" category, we have used in particular:

Last update on November 22, 2020

The last changes in the "Units of length" category were implemented by Stefan Banse on November 22, 2020. The main changes were:

  • November 5, 2020: Publication of the Length converter
  • Editorial revision of all texts in this category