📏 Length & Distance Converter

01. One number converts into 64 units of length at once

There's no target unit to pick. Every result appears as you type, so you can decide which one you needed afterwards.

02. Eight families of units, from metric to the Planck length

Metric, astronomical, imperial, Japanese traditional and its derivatives, typography, nautical and physics units are all covered, so cross-field comparisons happen in place.

03. Japanese traditional units are included in full

From rin to ri, the traditional Japanese measures are all here, which helps when reading dimensions on older plans.

04. Every figure updates the moment you type

Change the input and all 64 results recalculate, making it easy to feel your way toward the value you want.

05. Copy any result with a single click

Take the unit you need straight to your clipboard, with no risk of mistyping a long string of digits.

01. Basic Usage

1. Enter the value you want to convert
2. Select the input unit from the dropdown (default: meter)
3. All 64 unit conversions are displayed instantly by category
4. Click the copy button next to any value to copy it

02. Looking Up a Unit

1. Hover over the info icon to the left of a unit name to see additional information (tap on mobile)
2. Click the link icon at the right end of each row to view the Wikipedia article

Q. Why are some results shown in scientific notation?

A. Very large values (over 1 trillion) or very small values (below 0.0000000001) are displayed in scientific notation (e.g., 1.234567e+15) for readability.

Q. How far do SI prefixes go?

A. This tool supports all SI prefixes including the newest ones added in 2022. The smallest is quecto (10⁻³⁰) and the largest is quetta (10³⁰). While everyday use typically involves milli to kilo, scientific fields frequently use nano, pico, and femto.

Q. How many centimeters is 1 inch?

A. 1 inch = 2.54 centimeters exactly. This was internationally defined in 1959, and feet (12 inches) and yards (3 feet) are based on this definition.

Q. How many centimeters is 1 foot?

A. 1 foot = 30.48 centimeters. Since 1 foot = 12 inches, it's 2.54 × 12 = 30.48 cm. In aviation, altitude is measured in feet, with 1,000 feet ≈ 305 m.

Q. How many kilometers is 1 mile?

A. 1 mile = 1.609344 kilometers. A marathon distance (42.195 km) equals approximately 26.2 miles.

Q. What is a 'shaku'?

A. A Japanese traditional unit, approximately 30.303 cm (officially defined as 10/33 meter). Also called 'kanejaku', it's still used in traditional architecture and woodworking. A tatami mat's long side is typically 6 shaku (about 182 cm).

Q. What is a 'ken' and how does it relate to tatami?

A. 1 ken = 6 shaku ≈ 1.818 m. A standard tatami mat is 1 ken × 0.5 ken (3 shaku), and a 6-tatami room is approximately 9.9 square meters. However, tatami sizes vary by region (Kyoma, Chukyoma, Edoma, etc.).

Q. What is a 'kujirajaku'?

A. A Japanese unit for kimono tailoring, 1.25 times a regular shaku (about 37.88 cm). The name possibly derives from rulers made from whale baleen.

Q. What is an ångström?

A. 1 ångström (Å) = 0.1 nanometer = 100 picometers. It's convenient for expressing atomic and molecular sizes - a hydrogen atom's radius is about 0.53 Å, and carbon-carbon bonds are about 1.5 Å. Commonly used in crystallography and X-ray diffraction.

Q. What is an Astronomical Unit (AU)?

A. The average distance from Earth to the Sun, exactly 149,597,870,700 meters (about 149.6 million km). Useful for solar system distances: Mars is about 1.5 AU, Jupiter about 5.2 AU, and Pluto about 40 AU from the Sun.

Q. What's the difference between light-year and parsec?

A. A light-year is the distance light travels in one year (~9.46 trillion km = ~63,241 AU). A parsec means "parallax of one arcsecond" and equals about 3.26 light-years. Parsecs directly relate to astronomical distance measurement - if a star's annual parallax is 0.1 arcseconds, its distance is 10 parsecs. The nearest star, Proxima Centauri, is about 4.24 light-years ≈ 1.30 parsecs away.

Q. What is a nautical mile?

A. 1 nautical mile = 1,852 meters. Defined as one minute of latitude (1/60 of a degree). Used in navigation and aviation, and the unit "knot" means one nautical mile per hour.

Q. What is a fathom?

A. 1 fathom = 6 feet ≈ 1.83 meters. Primarily used for measuring water depth. The word comes from "the span of outstretched arms" and was also used for measuring anchor chains and fishing lines.

Q. What are points and picas?

A. Typography units. 1 point ≈ 0.353 mm (1/72 inch) and is the standard for font sizes. 1 pica = 12 points ≈ 4.23 mm, used for setting line spacing and margins.

Q. What are chains and furlongs?

A. British/American surveying and distance units. 1 chain = 66 feet ≈ 20.1 m, was the basic unit for land surveying (1 acre = 10 square chains). 1 furlong = 10 chains = 220 yards ≈ 201 m, still used in horse racing distances.

01. The Birth and Evolution of the Metric System

The metric system was born during the French Revolution in the 1790s. At that time, France alone had hundreds of different length units, with each region using different standards that hindered commerce. The revolutionary government aimed to create a universal system of units under the slogan " For all times, for all peoples." Initially, one meter was defined as "one ten-millionth of the distance from the North Pole to the Equator along a meridian." French astronomers Delambre and Méchain spent six years surveying the meridian from Dunkirk to Barcelona, and in 1799, the " Prototype Meter" - a platinum bar - was created. However, physical artifacts are subject to deterioration and damage over time. In 1960, the definition was changed to one based on the wavelength of light emitted by krypton-86 atoms. Then in 1983, the current definition was adopted: "the distance light travels in vacuum in 1/299,792,458 seconds." Since the speed of light is a fundamental constant of the universe, this makes the meter a universal and reproducible definition.

02. The History of SI Prefixes

SI prefixes have been expanded in stages. In 1795, kilo, hecto, deka, deci, centi, and milli were introduced. In 1960, micro through tera were added. As science and technology advanced, zepto, zetta, yocto, and yotta were added in 1991, and the newest prefixes - quecto, ronto, ronna, and quetta - were added in 2022. These names derive from Greek and Latin. For example, "kilo" comes from the Greek word for "thousand," and "milli" from the Latin for "one-thousandth." The newest prefixes "quecto" and "quetta" are variations of the Latin and Greek words for "ten."

03. Japanese Shaku-Kan System

The shaku-kan system was established by the Taihō Code in 701 AD, but its origins trace back to China's Zhou Dynasty (around the 11th century BCE). When first introduced to Japan, it was based on the Chinese Tang dynasty shaku (about 30 cm), but it developed uniquely over time. The kanji character for "shaku" (尺) is a pictograph representing the span between the thumb and index finger when spread apart. Indeed, one shaku roughly corresponds to this hand span. "Ken" (間) represents the spacing between pillars in architecture and became the basis for tatami mat sizes. "Ri" (里) originated from China but was defined at approximately 3.9 km in Japan. The kujirajaku is a unit exclusively for kimono tailoring, measuring 1.25 times the standard shaku (about 37.88 cm). There are various theories about the origin of its name - one suggests it derives from rulers made from whale baleen, while another proposes it comes from the verb "kujiru" (to work or rub) used when tailoring fabric. Although the shaku-kan system was officially abolished by the 1958 Measurement Law revision, it continues to be used in certain fields including architecture, kimono tailoring, and real estate.

04. Origins of the Imperial System

Imperial units have fascinating origins based on the human body. "Inch" derives from thumb width, "foot" from the length of a foot, "yard" from the distance from nose to fingertip with arm extended, and "fathom" from the span of outstretched arms. Legend has it that King Edward II of England defined one inch as "the length of three barleycorns placed end to end," and that Henry I decreed one yard to be "the distance from his nose to his fingertip." In 1959, English-speaking countries internationally defined 1 inch as exactly 2.54 cm, unifying the slightly different inches that had existed in each country. Today, the imperial system is used daily in the United States, United Kingdom, and Canada. In America, height is measured in feet and inches, and road distances in miles. In aviation, altitude is still measured in feet and speed in knots as the international standard.

05. Nautical Miles and Navigation

The nautical mile was created for navigation. One nautical mile is defined as the distance corresponding to one minute of latitude (1/60 of a degree). This allows distances to be read directly from the latitude scale on nautical charts. Since Earth is not a perfect sphere but an oblate spheroid (slightly flattened at the poles and bulging at the equator), the distance of one minute of latitude varies slightly by location (approximately 1,842m to 1,862m). At an international conference in 1929, one nautical mile was defined as exactly 1,852 meters, which corresponds to the value at approximately 45 degrees latitude. The speed unit "knot" means one nautical mile per hour, and its name derives from the "knotted rope" that sailors used. A rope with knots tied at regular intervals was trailed in the water, and speed was measured by counting how many knots passed in a set time.

06. Astronomical Units and Cosmic Scales

The Astronomical Unit (AU) is a convenient unit for expressing distances within the solar system. One AU is the average distance between Earth and the Sun, precisely defined as 149,597,870,700 meters. Light takes approximately 8 minutes and 19 seconds to travel this distance. A light-year is the distance light travels in one year, approximately 9.46 trillion km. Despite having "year" in its name, it's a unit of distance, not time. The nearest star, Proxima Centauri, is about 4.24 light-years away - meaning the light we see from it today was emitted over 4 years ago. The parsec is short for "parallax second" and directly relates to how astronomers measure distances. As Earth orbits the Sun, nearby stars appear to shift slightly against the background of more distant stars (annual parallax). The distance at which this parallax equals one arcsecond is one parsec, equivalent to about 3.26 light-years. If a star's parallax is 0.1 arcseconds, its distance is 10 parsecs; if 0.01 arcseconds, 100 parsecs. This is why astronomers often prefer parsecs to light-years.

07. The Origin of the Ångström

The ångström (Å) is named after Swedish physicist Anders Jonas Ångström (1814-1874). He precisely measured the spectrum of sunlight and expressed wavelengths in units of 10⁻¹⁰ meters, which led to widespread adoption of this unit. One ångström equals 0.1 nanometer or 100 picometers - a convenient size for expressing atomic and molecular dimensions. A hydrogen atom's diameter is about 1 Å, and visible light wavelengths range from about 4000 to 7000 Å. Although not an official SI unit, the ångström remains widely used in crystallography, spectroscopy, and semiconductor engineering.

08. The Surprising "Retrofitted" History of SI Units

The SI unit system appears scientific and rigorous, but it actually has a long history of being "retrofitted" to maintain consistency with earlier definitions. Consider the meter's definition: "the distance light travels in vacuum in 1/299,792,458 seconds." That oddly specific number 299,792,458 was calculated backwards to exactly match the old prototype meter bar. In other words, rather than redefining "what one meter is" scientifically, they chose to set the speed of light at 299,792,458 m/s to preserve the existing meter. Similarly, the "second" was originally defined as "1/86,400 of the time it takes Earth to rotate once." However, Earth's rotation isn't constant—it's actually slowing down due to tidal forces. So in 1967, the definition was changed to be based on cesium atomic vibrations, but that specific number of 9,192,631,770 oscillations was chosen to match the old "second." The kilogram had an surprisingly primitive definition until 2019: "the mass of a metal cylinder stored in Paris." For over 130 years, all mass measurements worldwide were ultimately compared to the " International Prototype Kilogram" kept in a vault in France. While it's now defined using Planck's constant, that value too was chosen to match the historical kilogram. Even the kelvin was based on the triple point of water (273.16 K), specifically to maintain compatibility with the Celsius scale's 0°C and 100°C reference points. Looking at it this way, the "universal and scientific" SI system is really just historical human conventions that have been "scientifically redefined." Rather than fundamental truths of the universe, it's a grand patchwork of accumulated human customs with scientific justifications retrofitted onto them.

09. Units of the Printing World

The point was born in the letterpress era to describe the size of metal type, taking its name from the Latin punctum (point). Today the international standard is 1 point = 1/72 inch (about 0.35 mm), with body text typically set at 10-12 points and headings at 18-24 points. The pica equals 12 points (about 4.23 mm) and is used in DTP for column widths, line spacing, and margins. Its name comes from the Medieval Latin pica (magpie), after a typeface used in church rule books — one theory holds that the bird's black-and-white plumage evoked the look of a printed page. The same word "point" once meant slightly different lengths depending on the country and the trade. Europe long used the Didot point (about 0.376 mm), while Japanese phototypesetting adopted its own unit called the " Q," set at exactly 0.25 mm so that it would sit neatly within the metric system.

10. Everyday Things That Became Units

The furlong, familiar from horse racing, is 220 yards (about 201 m). Its name comes from the Old English furh (furrow) and lang (long), describing the length of a furrow a team of oxen could plow in one go. A mile is exactly eight furlongs because medieval field divisions became the basis for the mile itself. The chain traces back to the 100-link surveying chain devised by Edmund Gunter in 1620, and measures 22 yards (about 20.1 m). Since one acre equals 10 square chains, a single tool could handle both surveying and area calculation. A cricket pitch is exactly one chain — a leftover from the days when the unit was in wide use. The hand comes from the width of a palm and equals 4 inches (about 10.2 cm). Used since ancient Egypt to measure the height of horses, it remains standard in British and American racing. Its notation is peculiar: "15.2 hands" does not mean 15.2 times the unit, but "15 hands and 2 inches."