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Length Converter

1Meter = 100Centimeter
100

International System (SI)

Picometer (pm)1.00×10¹²
Nanometer (nm)1.00×10⁹
Micrometer (μm)1000000
Millimeter (mm)1000
Centimeter (cm)100
Decimeter (dm)10
Meter (m)1
Kilometer (km)0.001
Astronomical Unit (AU)6.68×10⁻¹²
Light Year (ly)1.06×10⁻¹⁶

Imperial

Mil (mil)39370.07874
Inch (in)39.370079
Foot (ft)3.28084
Yard (yd)1.093613
Mile (mi)0.000621
Nautical Mile (nmi)0.00054
Fathom (fm)0.546807
Furlong (fur)0.004971

Chinese Market

Li0.002
Zhang0.3
Chi3
Cun30
Fen300
Hao3000

Free online length converter. 24 units, 5 families. Pick any two, get an instant result. Local compute, no upload.

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About length, distance, and the units behind them

Length is one of the seven base quantities of the International System of Units (SI), defined by the meter (m). Since 1983 the meter is defined as the distance light travels in vacuum in 1/299,792,458 of a second, which means every other length unit on this page - inch, foot, mile, nautical mile, light-year, chi, cun - is a fixed or convention-defined multiple of that single standard.

Metric prefixes let one meter cover everything from the atomic scale to interplanetary distances without switching units: 1 picometer (pm) = 10⁻¹² m is roughly the size of an atomic nucleus; 1 kilometer (km) = 10³ m handles everyday travel. Beyond that, 1 astronomical unit (AU) ≈ 1.496 × 10⁸ km serves the Earth-Moon and inner-solar-system scales; 1 light-year (ly) ≈ 9.461 × 10¹² km is for stars. This tool lets you jump freely between these scales.

Imperial / US customary units are still in everyday use in the United States and partly in the UK. The 1959 international yard-and-pound agreement fixed 1 inch (in) = 0.0254 m, 1 foot (ft) = 0.3048 m, 1 yard (yd) = 0.9144 m, 1 mile (mi) = 1760 yards = 1609.344 m. The nautical mile (nmi) = 1852 m is defined independently and is used in maritime and aviation because it matches one minute of latitude.

Chinese traditional length units have several thousand years of history. The late-Qing / Republic-era and modern standard is 1 chi = 1/3 m, 1 cun = 1/10 chi, 1 zhang = 10 chi ≈ 3.33 m, 1 li = 1800 chi = 500 m. These units remain common in colloquial speech, TCM (Traditional Chinese Medicine) dose descriptions, and classical literature. This tool follows the modern standard, so all conversions to and from metric are exact.

The astronomical unit (AU) and the light-year (ly) are the two key scales beyond the solar system. Since 2012 AU is defined as exactly 149,597,870,700 m, roughly the Earth-Sun mean distance, used in spacecraft navigation and planetary orbit mechanics; 1 light-year = 9,460,730,472,580,800 m, the distance light travels in one Julian year. The nearest star system (Proxima Centauri) is about 4.24 light-years away; the Milky Way is roughly 100,000 light-years across.

All conversions on this page are pure linear scaling - there is no offset like with temperature. So a single factor is enough: target = source × (source_factor / target_factor). The factors are precomputed once, and each conversion is just a double-precision multiply and divide; only when the number is extreme (below 10⁻⁶ or above 10⁹) does the display switch to scientific notation.

Use Cases

  • Shopping for clothes, screens, furniture on US / international sites: convert inches / feet into cm / m
  • Filling out forms that only accept metric units: convert feet / inches into meters / centimeters
  • Running, cycling, marathon training: convert kilometers and statute miles back and forth
  • Reading nautical charts, aviation charts, or flight plans: convert kilometers into nautical miles
  • Doing astronomy homework or science writing: convert light-years into kilometers or AU
  • Real estate, furniture, fabric, calligraphy and painting: convert Chinese zhang / chi / cun into meters
  • Engineering and design on drawings or 3D-print specs: switch between mm / cm / m / in / ft
  • Surveying and map reading: switch among mi / km / nmi / fur / fm
  • DIY, woodworking, sewing, scale modelling: convert mm to inches (or back)
  • Hit 'Show all conversions' to see your value in every length unit at once for side-by-side comparison
  • Home renovation, furniture fitting, bathroom remodeling: convert panel, pipe-run, window-sill, shower-arm distances from blueprints (mm/m) into onsite feet/inches to avoid half-centimeter rework
  • In BIM / CAD projects: align international team drawings in inch/mm with local team drawings in cm/m so model exports and site layouts line up
  • Cross-border e-commerce SKU dimensions, freight cubic calculations, and educational height-comparison charts - any micro-table where length IS the data - all run in one expanded-view pass on this tool

How to Use

  1. Type a number into the left input box (default is 1).
  2. Pick the source unit from the left dropdown - SI, imperial, nautical, astronomical, or Chinese traditional are all available.
  3. Pick the target unit from the right dropdown; the converted value appears instantly.
  4. Click the swap button between the dropdowns to flip source and target, then read the inverse value.
  5. Click 'Show all conversions' to see your value in every length unit at once, grouped by family.

Features

  • 24 length units across 5 families: metric, imperial/US customary, nautical mile, astronomical units, and Chinese traditional (li, zhang, chi, cun, fen, hao)
  • Bidirectional conversion between any two units: switch the dropdowns and the result updates in real time
  • One-click all-units panel: every unit in the same category is computed at once, grouped by family
  • Mid-button swap: flip source and target with one click - the inverse result computes without retyping
  • Astronomy-scale coverage: includes astronomical unit (AU) and light-year (ly) for science and astronomy use
  • Scientific notation for tiny / huge values: pm-to-m and km-to-ly conversions automatically use superscript exponents so the digits stay readable
  • Chinese traditional units: li, zhang, chi, cun, fen, hao for everyday and TCM-context use
  • Pure browser-side compute: every conversion runs locally via fixed factors - no network request, nothing leaves your device

Two length entry points on this site - which one do I want?

There are two ways to handle length on this site. Pick the one that matches what you actually need, so you don't waste time on the wrong page.

ToolWhat it doesBest for
This page: the Length ConverterSingle-category length converter covering 5 families and 24 units (SI, imperial, nautical, astronomical, Chinese traditional).Use this when the conversion is specifically length / distance. Pick this page when you need deep coverage on AU, ly, nautical miles, or Chinese traditional units - depth the aggregator page flattens.
Aggregator (Unit Converter)Aggregator page across 35 categories: length, mass, temperature, area, volume, speed, time, pressure, energy, data storage, and more.Use the aggregator when you don't yet know which category a value belongs to, or when you routinely bounce between unrelated categories. This length page is a vertical deep-dive split out from that aggregator.

Best Practices

Anchor every conversion on the SI meter (m) in your head for fast sanity-check

Length is a pure linear quantity, so every conversion is essentially a precise multiple of the meter. If you doubt a result, convert both units to meters first and compare: 1 ft / 1 in = 0.3048 / 0.0254 = 12 exactly. This takes a second and catches most rounding mistakes.

Use nautical miles (nmi) - not statute miles - in maritime and aviation

A nautical mile is exactly 1852 m, chosen so 60 nmi = 1° of latitude. Nautical charts, flight plans, and GPS waypoints all use nautical miles. Substituting 1609.344 m statute miles adds a ~15% error - more than enough to misplace a navigation fix. This tool's dropdown keeps both available side-by-side, so a single click is enough to switch.

Use AU inside the solar system, light-years for stars and beyond

AU for planets, asteroids, spacecraft; light-years for stars and further out. Mixing the two inside the same paragraph is technically correct but reads as unprofessional - 1 ly ≈ 63,241 AU is four orders of magnitude. Deep-sky astronomy also uses parsec (pc): 1 pc ≈ 3.262 ly.

Keep both mm and inches handy for DIY and craft work

Screws, lumber, fabric, 3D-print filament diameters are mm in the metric world but inches (often fractional, like 1/4", 3/8") in the US. Memorize a couple of anchors - 1 in = 25.4 mm, 1 mm ≈ 0.0394 in, 1 cm = 10 mm - and you eliminate most everyday mistakes.

For Chinese traditional chi: confirm the dynasty before you conclude

Tang-dynasty chi was shorter than Qing-dynasty chi; the modern Republic-era standard reset the value again. This tool uses the late-Qing / Republic-era and modern 1 chi = 1/3 m. If you are working on historical documents, confirm that era's chi first; do not blindly plug into the modern standard.

FAQ

How many centimeters are in one inch? And how many inches in one centimeter?

By international definition, 1 inch = 2.54 cm (exact). So 1 in = 2.54 cm, and conversely 1 cm ≈ 0.3937 in. Common references: 10 cm ≈ 3.937 in, 50 cm ≈ 19.685 in, 100 cm (1 m) ≈ 39.37 in.

How many meters in one foot? How many feet in one meter?

1 ft = 0.3048 m (exact). So 1 m ≈ 3.2808 ft. Common references: 1.5 m ≈ 4.92 ft, 1.7 m ≈ 5.58 ft (≈ 5 ft 7 in), 1.8 m ≈ 5.91 ft.

How many miles in one kilometer? And kilometers in one mile?

1 mi ≈ 1.609344 km, and 1 km ≈ 0.621371 mi. Quick references: 5 km ≈ 3.11 mi (a typical 5K race distance), 100 km ≈ 62.14 mi, a full marathon ≈ 42.195 km ≈ 26.2 mi.

How do you convert kilometers and nautical miles?

1 nautical mile = 1852 m = 1.852 km, so 1 km ≈ 0.539957 nmi. Nautical miles are used in maritime, aviation, and polar routes - the unit was originally defined as one minute of latitude along any meridian, so 60 nmi = 1° of latitude.

What is a light-year? How many km is one light-year?

1 light-year ≈ 9.461 × 10¹² km, the distance light travels in 1 Julian year (365.25 days) at 299,792,458 m/s. Light-years describe distances to stars and galaxies - for example, the nearest star system (Proxima Centauri) is about 4.24 light-years away.

What is the difference between AU and light-year?

1 AU ≈ 149,597,870.7 km - the average Earth-Sun distance, used within the solar system. 1 light-year ≈ 63,241 AU, used for stellar distances. Astronomers pick the unit that keeps the numbers readable: AU for planets, light-years for stars, parsecs (pc) for stellar/galactic scales.

How many chi (feet) in a meter? How many cun (inches) in a chi?

Chinese traditional length units were not standardized across dynasties. This tool uses the late-Qing / Republic-era and modern standard: 1 chi = 1/3 m ≈ 33.33 cm, 1 cun = 1/10 chi ≈ 3.33 cm, 1 zhang = 10 chi ≈ 3.33 m, 1 li = 1800 chi = 500 m, 1 fen = 1/10 cun ≈ 3.33 mm, 1 hao = 1/10 fen ≈ 0.333 mm. This standard remains the most widely used in mainland China, Taiwan, Hong Kong, and TCM (Traditional Chinese Medicine) contexts.

Are UK statute miles and US miles the same unit?

In this tool, both the UK statute mile and the US mile (as in road signs) are defined as exactly 1609.344 m. The US also uses a separate 'US survey mile' of about 1609.347 m for legacy land surveys; the difference (~3 mm per mile) only matters for high-precision surveying and can be ignored in everyday use.

How accurate is the conversion?

Every conversion is computed from double-precision IEEE 754 floating-point, with factors anchored on the official SI definitions (1 in = 0.0254 m, 1 ft = 0.3048 m, 1 ly = 9.4607304725808 × 10¹⁵ m, etc.). The display rounds with parseFloat(num.toFixed(6)), so everyday lengths have a relative error well below one part per million.

Can I swap the source and target units with one click?

Yes. The swap button between the two dropdowns flips source and target instantly and recomputes - you can see the inverse conversion without retyping the number.

Why do very small or very large numbers show in scientific notation?

Any absolute value below 0.000001 (for example pm ↔ m) or above 10⁹ (for example km ↔ ly) is rendered in scientific notation with an exponent so the digits stay readable. The underlying number stays full double precision; only the display format changes.

Can I use this offline?

Yes. After the page loads, every conversion runs locally in the browser using built-in factors - no API call, no network dependency. Works in a plane, in a workshop, or anywhere without a connection.

Troubleshooting

Result is off by 10x, 100x, or 1000x?

First check whether you selected the source / target units you actually meant. The most common mistakes: mm / cm (10×), km / m (1000×), mi / nmi (~16%). Expand the 'all conversions' panel - if the other units look right, the issue is in your selection, not in the conversion factor.

Why does the result use scientific notation (for example 1.23 × 10⁻⁵)?

Picometer-scale or light-year-scale conversions use exponent notation so the digits stay readable. The underlying value is still full double precision; only the display format changes. If you need a plain decimal, switch the target unit to a friendlier magnitude (m → km instead of m → pm).

Why does 1 chi show as ≈ 33.33 cm and not 33.0 cm or 32.0 cm?

Chinese traditional length units varied across dynasties. This tool uses 1 chi = 1/3 m exactly, the late-Qing / Republic-era and modern standard that remains the most common in mainland China, Taiwan, and Hong Kong. For historical documents, confirm that era's chi value before drawing conclusions.

Nautical mile (nmi) and statute mile (mi) look the same on the map - what now?

1 nautical mile = 1852 m, 1 statute mile = 1609.344 m, the former ~15% larger. Nautical charts, aviation charts, and flight plans use nautical miles; road signs and running events use statute miles. Mixing them up at scale (for example 100 nmi) costs tens of kilometers in navigation precision. This tool labels them 'nmi' and 'mi' in the dropdowns - do not pick by the words 'nautical' / 'mile' alone.

The page shows 'invalid input' or the result is NaN?

Usually a non-numeric character was entered (commas, spaces, Chinese punctuation, unit symbols). The dropdowns already carry the unit, so do not add a unit after the number. The right pattern: type '1', pick 'm' in source, pick 'ft' in target. If it still fails, refresh the page or try a different browser.

Glossary

Meter (m)
The SI base length unit, defined since 1983 as the distance light travels in vacuum in 1/299,792,458 of a second. Every other length unit on this page is an exact multiple of the meter.
Inch (in)
Imperial / US customary length unit, defined since 1959 as exactly 0.0254 m. 12 inches = 1 foot.
Foot (ft)
Imperial / US customary length unit, defined as exactly 0.3048 m = 12 inches.
Yard (yd) / Fathom (fm) / Furlong (fur)
Yard (yd) = 0.9144 m = 3 feet, used mainly for US fabric and athletics track lengths. Fathom (fm) = 1.8288 m = 6 feet, a maritime depth unit. Furlong (fur) = 201.168 m = 1/8 mile, mainly used in horse racing (1 furlong = 1/8 mile) and historical land survey. All three are sub-units of the imperial length family and serve maritime / historical / specialist contexts.
Mile (mi)
Imperial / US customary length unit, defined as exactly 1609.344 m = 1760 yards.
Nautical mile (nmi)
Maritime and aviation distance unit, defined as exactly 1852 m. The size was chosen so 1 nautical mile = 1 minute of latitude along any meridian, so 60 nmi = 1° of latitude, lining up naturally with nautical charts, flight plans, and GPS waypoints. Note: nautical mile (nmi) ≠ statute mile (mi), which is 1609.344 m.
Astronomical unit (AU) / Light-year (ly)
Since 2012 the AU is defined as exactly 149,597,870,700 m, roughly the Earth-Sun mean distance, used for inner-solar-system planetary orbits and spacecraft navigation. A light-year (ly) is the distance light travels in one Julian year, about 9.4607 × 10¹⁵ m ≈ 63,241 AU, used to describe stars and galaxies. Both are anchored on the SI meter definition; AU is for 'within the solar system', ly for 'stellar and beyond' - a four-orders-of-magnitude gap.
Chi (尺) / Zhang (丈)
Chinese traditional length units. This tool uses 1 chi = 1/3 m ≈ 33.33 cm and 1 zhang = 10 chi ≈ 3.33 m, the late-Qing / Republic-era and modern standard still common in everyday speech, TCM (Traditional Chinese Medicine) acupoint location, and classical literature.
Cun (寸) / Li (里)
Cun (寸) = 1/10 chi ≈ 3.33 cm; li (里) = 1800 chi = 500 m. Both belong to the Chinese traditional length family. The cun is often colloquially equal to the width of a thumb joint, used for body-surface acupoint location in TCM; the li is the larger-scale colloquial distance unit.

Common length conversion anchors

Memorize this column and almost every everyday length becomes mental arithmetic.

FromToFactorCommon scene
1 cmin0.3937 inClothing, screens, school rulers
1 incm2.54 cmClothing, screens (exact SI)
1 mft3.2808 ftHeight, furniture dimensions
1 ftm0.3048 mHeight, room size (exact)
1 kmmi0.6214 miRunning, cycling, road travel
1 mikm1.6093 kmRoad travel, marathon distance
1 kmnmi0.5400 nmiMaritime / aviation planning
1 nmikm1.852 kmMaritime / aviation charts
1 AUkm1.496 × 10⁸ kmSolar-system distances
1 lykm9.461 × 10¹² kmInterstellar distances
1 zhangm3.333 mChinese traditional length
1 chicm33.33 cmChinese traditional length

Quick height lookup

Height is one of the most frequently converted lengths. This table lets you look up any common height in the units you need.

MetersCentimetersInches (approx)Feet / Inches
1.50 m150 cm59.06 in4 ft 11 in
1.60 m160 cm62.99 in5 ft 3 in
1.70 m170 cm66.93 in5 ft 7 in
1.75 m175 cm68.90 in5 ft 9 in
1.80 m180 cm70.87 in5 ft 11 in
1.85 m185 cm72.83 in6 ft 1 in
1.90 m190 cm74.80 in6 ft 3 in

Privacy & Security

Every length conversion on this page runs in your browser. The number you enter never leaves your device - no network request, no server log, and we do not analyze the values themselves. Close the tab and the input is gone; the tool does not persist any value to localStorage. Safe for sensitive working scenarios.

Authoritative References