Unit Converter
Convert between 100+ units across 11 categories — length, weight, temperature, area, volume, speed, time, digital storage, energy, pressure, and angle. Instant results with formula explanations and full conversion tables.
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Length Converter
Convert length and distance between 20 units — mm, cm, m, km, inches, feet, yards, miles, nautical miles, fathoms, light-years, astronomical units, and more. Instant results with formula, conversion factor, and full reference table.
Common Conversions
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Explore This Tool in Context
Length Converter is part of the Conversion Tools collection. If you want a broader view of similar workflows, open the Conversion Tools category page or browse all QuickTools categories.
Common next steps after this tool include Unit Converter, Area Converter and Speed Converter.
What Is a Length Converter?
A length converter is an online tool that instantly transforms any measurement of length or distance from one unit to another — no maths required. Whether you need to convert kilometres to miles for a road trip, centimetres to inches for a sewing pattern, or astronomical units to light-years for a science project, this tool covers you.
It supports 20 units spanning four systems: the metric (SI) system from picometres to kilometres, the imperial/US customary system from inches to leagues, nautical units used in aviation and sailing, and astronomical units used in astrophysics. All conversion factors are stored at full precision using internationally-defined exact values.
How to Use the Length Converter
- Quick conversions — tap one of the shortcut chips (km→mi, mi→km, m→ft, etc.) to pre-fill the most common pairs instantly.
- Choose units manually — use the From and To dropdowns, which are grouped by measurement system (Metric, Imperial, Nautical, Astronomical).
- Enter a value — type any number in the input field; the result updates live as you type.
- Swap direction — click ⇄ to reverse the conversion and reuse the result as the new input.
- Copy the result — hit the Copy button to copy the converted value to your clipboard.
- Browse all conversions — the All Conversions table shows your value in every unit at once. Use the group tabs (All / Metric / Imperial / Nautical / Astronomical) to filter, or click any row to set that unit as the new target.
Common Length Conversion Examples
| From | To | Result | Common Use |
|---|---|---|---|
| 1 kilometre | miles | 0.6213712 mi | Road distances |
| 1 mile | kilometres | 1.609344 km | Road distances |
| 1 metre | feet | 3.2808399 ft | Room dimensions |
| 1 foot | centimetres | 30.48 cm | Height / furniture |
| 1 inch | millimetres | 25.4 mm | Engineering / screens |
| 1 nautical mile | kilometres | 1.852 km | Aviation & sailing |
| 1 yard | metres | 0.9144 m | Sports fields |
| 1 light-year | kilometres | 9.4607 × 10¹² km | Astronomy |
| 100 cm | inches | 39.370079 in | Fashion / textiles |
| 5 km | miles | 3.1068560 mi | Running races |
| 1 astronomical unit | km | 1.495979 × 10⁸ km | Solar distances |
| 1 furlong | metres | 201.168 m | Horse racing |
How the Length Converter Works
Every unit of length is stored as an exact multiplier relative to the metre (the SI base unit). To convert from unit A to unit B, the calculator uses a two-step ratio:
result = value × factor(A) ÷ factor(B)
For example, to convert 5 miles → metres: 1 mile = 1609.344 m, 1 metre = 1 m, so result = 5 × 1609.344 ÷ 1 = 8046.72 m.
All factors are exact internationally-defined values (e.g. 1 inch = 25.4 mm exactly per the 1959 International Yard and Pound Agreement). Results are rounded to 10 significant figures to eliminate floating-point noise while preserving full scientific precision.
Length Unit Reference
🔬Metric (SI)
- pmPicometre— Atomic radii scale
- nmNanometre— Wavelengths of light
- µmMicrometre— Human hair width
- mmMillimetre— Ruler smallest division
- cmCentimetre— Height, clothing
- dmDecimetre— ≈ hand width
- mMetre— SI base unit
- kmKilometre— Road distances
🏈Imperial / US Customary
- inInch— 25.4 mm exactly
- ftFoot— 12 inches
- ydYard— 3 feet
- chChain— 66 ft, surveying
- furFurlong— 220 yd, horse racing
- miMile (statute)— 5280 ft
- leaLeague— 3 statute miles
⚓Nautical
- nmiNautical mile— 1852 m, aviation & sailing
- ftmFathom— 6 ft, water depth
🌌Astronomical
- auAstronomical Unit— Earth–Sun distance
- lyLight-year— ≈ 9.461 × 10¹² km
- pcParsec— ≈ 3.086 × 10¹³ km
Frequently Asked Questions
How many centimetres are in an inch?+
Exactly 2.54 cm. This is the internationally-defined exact value set in 1959. So 1 inch = 2.54 cm, and 1 cm = 0.393701 inches.
How do I convert feet and inches to centimetres?+
Multiply the feet by 30.48 and the inches by 2.54, then add the results. For example, 5 ft 10 in = (5 × 30.48) + (10 × 2.54) = 152.4 + 25.4 = 177.8 cm.
What is a nautical mile and why is it different from a regular mile?+
A nautical mile is exactly 1,852 metres (1.1508 statute miles). It was originally defined as one arcminute of latitude along a meridian of the Earth, making it natural for navigation. A statute mile is 1,609.344 metres and is used for road distances.
How many kilometres in a light-year?+
A light-year is approximately 9.4607 × 10¹² kilometres (about 9.46 trillion km). It is the distance light travels in one Julian year (365.25 days) at 299,792.458 km/s.
Is this converter accurate enough for engineering work?+
Yes. All conversion factors are exact (e.g. 1 inch = 25.4 mm) or at full IEEE 754 double-precision accuracy. Results are displayed to 10 significant figures, which far exceeds typical engineering tolerances.
What is a furlong?+
A furlong is 220 yards (660 feet or 201.168 metres). It originated as the length of a furrow in a ploughed field and is still used today in horse racing to express race distances.
What is a parsec?+
A parsec is about 3.0857 × 10¹³ km (roughly 3.26 light-years). It is defined as the distance at which one astronomical unit subtends an angle of one arcsecond and is the standard unit for stellar and galactic distances.
How is a kilometre different from a mile?+
A kilometre is 1,000 metres, while a mile is 1,609.344 metres. So 1 mile ≈ 1.609 km, and 1 km ≈ 0.621 miles. A quick mental shortcut: multiply km by 0.6 to get an approximate mileage.
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