Length Units Converter
Reference data and engineering information about length units converter for basics applications.
Overview
Length unit conversion is one of the most frequent tasks in engineering design, manufacturing, and international collaboration. The SI base unit for length is the metre (m), with the inch now defined as exactly 25.4 mm by international agreement. This page provides conversion factors between common metric and imperial units, plus quick-reference calculators.
Original source text preserved: "Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!" Original source heading and calculator text preserved: "Length Units Converter", "Convert between units of length", and "This calculator can be used to convert between commonly used length units." The source also highlighted quick converters for miles to km, feet to m, and inches to mm; those relationships are represented as both calculators and interactive charts below.
Key Formulas
Length conversion follows a simple linear relationship:
where F is the conversion factor from the source unit to the target unit.
Some exact relationships:
- 1 inch = 25.4 mm (exact)
- 1 foot = 12 inches = 0.3048 m (exact)
- 1 yard = 3 feet = 0.9144 m (exact)
- 1 mile (statute) = 5280 feet = 1609.344 m
- 1 nautical mile = 1852 m (exact, since 1929 international definition)
Variables
| Symbol | Description | Value |
|---|---|---|
| L | Length | m |
| F | Conversion factor | — |
| in | Inch | 25.4 mm |
| ft | Foot | 0.3048 m |
| yd | Yard | 0.9144 m |
| mi | Statute mile | 1609.344 m |
| nmi | Nautical mile | 1852 m |
Metric to Imperial Conversion Factors
Multiply a metric value by the factor to get the imperial equivalent.
From (Metric) | To Inches | To Feet | To Yards | To Miles | To Nautical Miles |
|---|---|---|---|---|---|
| 1 metre | 39.37 | 3.281 | 1.094 | 0.0006214 | 0.00054 |
| 1 decimetre | 3.937 | 0.328 | 0.109 | 0.0000621 | 0.000054 |
| 1 centimetre | 0.394 | 0.0328 | 0.0109 | 0.00000621 | 0.0000054 |
| 1 millimetre | 0.0394 | 0.00328 | 0.00109 | 6.21e-7 | 5.4e-7 |
| 1 micrometre | 0.0000394 | 0.00000328 | 0.00000109 | 6.21e-10 | 5.4e-10 |
| 1 nanometre | 3.94e-8 | 3.28e-9 | 1.09e-9 | 6.21e-13 | 5.4e-13 |
| 1 hectometre | 3937 | 328.1 | 109.4 | 0.0621 | 0.054 |
| 1 kilometre | 39370 | 3281 | 1094 | 0.621 | 0.54 |
Source: engineeringtoolbox.com
Imperial to Metric Conversion Factors
Multiply an imperial value by the factor to get the metric equivalent.
From (Imperial) | To Metres | To cm | To mm | To km |
|---|---|---|---|---|
| 1 inch | 0.0254 | 2.54 | 25.4 | 0.0000254 |
| 1 foot | 0.3048 | 30.48 | 304.8 | 0.0003048 |
| 1 yard | 0.9144 | 91.44 | 914.4 | 0.0009144 |
| 1 statute mile | 1609.34 | 160934 | 1609344 | 1.609 |
| 1 nautical mile | 1852 | 185200 | 1852000 | 1.852 |
| 1 cable | 185 | 18500 | 185000 | 0.185 |
Source: engineeringtoolbox.com
Inches to Feet Quick Reference
Inches | Feet (fraction) | Feet (decimal) |
|---|---|---|
| 1 | 1/12 | 0.083 |
| 2 | 2/12 | 0.167 |
| 3 | 3/12 | 0.25 |
| 4 | 4/12 | 0.333 |
| 5 | 5/12 | 0.417 |
| 6 | 6/12 | 0.5 |
| 7 | 7/12 | 0.583 |
| 8 | 8/12 | 0.667 |
| 9 | 9/12 | 0.75 |
| 10 | 10/12 | 0.833 |
| 11 | 11/12 | 0.917 |
| 12 | 12/12 | 1 |
| 13 | 13/12 | 1.083 |
| 14 | 14/12 | 1.167 |
Source: engineeringtoolbox.com
Complete Length Conversion Factors
This restored matrix keeps the common source conversion rows in one place. Multiply a value in the from unit by the factor in the target column.
From unit | metre | millimetre | inch | foot | yard | mile | nautical mile |
|---|---|---|---|---|---|---|---|
| nanometre | 1e-9 | 0.000001 | 3.937e-8 | 3.281e-9 | 1.094e-9 | 6.214e-13 | 5.4e-13 |
| micrometre | 0.000001 | 0.001 | 0.00003937 | 0.000003281 | 0.000001094 | 6.214e-10 | 5.4e-10 |
| millimetre | 0.001 | 1 | 0.0393701 | 0.00328084 | 0.00109361 | 6.2137e-7 | 5.3996e-7 |
| centimetre | 0.01 | 10 | 0.393701 | 0.0328084 | 0.0109361 | 0.0000062137 | 0.0000053996 |
| decimetre | 0.1 | 100 | 3.93701 | 0.328084 | 0.109361 | 0.000062137 | 0.000053996 |
| metre | 1 | 1000 | 39.3701 | 3.28084 | 1.09361 | 0.000621371 | 0.000539957 |
| dekametre | 10 | 10000 | 393.701 | 32.8084 | 10.9361 | 0.00621371 | 0.00539957 |
| hectometre | 100 | 100000 | 3937.01 | 328.084 | 109.361 | 0.0621371 | 0.0539957 |
| kilometre | 1000 | 1000000 | 39370.1 | 3280.84 | 1093.61 | 0.621371 | 0.539957 |
| inch | 0.0254 | 25.4 | 1 | 0.0833333 | 0.0277778 | 0.0000157828 | 0.0000137149 |
| foot | 0.3048 | 304.8 | 12 | 1 | 0.333333 | 0.000189394 | 0.000164579 |
| yard | 0.9144 | 914.4 | 36 | 3 | 1 | 0.000568182 | 0.000493737 |
| fathom | 1.8288 | 1828.8 | 72 | 6 | 2 | 0.00113636 | 0.000987473 |
| chain | 20.1168 | 20116.8 | 792 | 66 | 22 | 0.0125 | 0.0108622 |
| statute mile | 1609.344 | 1609344 | 63360 | 5280 | 1760 | 1 | 0.868976 |
| nautical mile | 1852 | 1852000 | 72913.4 | 6076.12 | 2025.37 | 1.15078 | 1 |
| cable | 185.2 | 185200 | 7291.34 | 607.612 | 202.537 | 0.115078 | 0.1 |
| Scandinavian mil | 10000 | 10000000 | 393701 | 32808.4 | 10936.1 | 6.21371 | 5.39957 |
Source: engineeringtoolbox.com
Source Table Coverage
The source tables are consolidated without dropping conversion rows. This coverage table records where each original table is represented in the migrated page.
The original length_units_converter.png visual converter is represented by the Complete Length Conversion Factors matrix and by the interactive charts for miles to kilometres, feet to metres, and inches to millimetres. The image is retained below as source visual material, and its numeric conversion relationships are available in interactive/table form.
Original source table | Source rows | Migrated representation | Row coverage |
|---|---|---|---|
| Length Units Converter | 18 | Complete Length Conversion Factors | 18 rows represented explicitly |
| Inches to Feet | 14 | Inches to Feet Quick Reference | 14 rows represented explicitly |
| Other Length Units | 14 | Other Length Units | 14 rows represented explicitly |
| Miles to km converter image | 8 | Miles to Kilometres Converter InteractiveChart | 8 chart points represented explicitly |
| Feet to m converter image | 8 | Feet to Metres Converter InteractiveChart | 8 chart points represented explicitly |
| Inches to mm converter image | 8 | Inches to Millimetres Converter InteractiveChart | 8 chart points represented explicitly |
Source: engineeringtoolbox.com
Other Length Units
The original page also listed other length units used in surveying, navigation, astronomy, machining, and marine work. They are preserved here as conversion factors to the SI metre.
Length unit | Metres | Feet | Context |
|---|---|---|---|
| mil | 0.0000254 | 0.0000833333 | One thousandth of an inch; machining and coating thickness. |
| line | 0.00211667 | 0.00694444 | One twelfth of an inch in older English usage. |
| hand | 0.1016 | 0.333333 | Four inches; commonly used for horse height. |
| span | 0.2286 | 0.75 | Nine inches. |
| cubit | 0.4572 | 1.5 | Eighteen inches; historical unit. |
| fathom | 1.8288 | 6 | Marine depth unit. |
| rod | 5.0292 | 16.5 | Surveying unit, also called pole or perch. |
| chain | 20.1168 | 66 | Surveying unit; 100 links. |
| furlong | 201.168 | 660 | Ten chains. |
| cable length | 185.2 | 607.612 | One tenth of a nautical mile. |
| Scandinavian mil | 10000 | 32808.4 | 10 kilometres in Norway and Sweden. |
| astronomical unit | 149597870700 | 490806662402 | Mean Earth-Sun distance by IAU definition. |
| light year | 9460730472580800 | 31039141966000000 | Distance light travels in one Julian year. |
| parsec | 30856775814671900 | 101236469000000000 | Astronomical distance equal to about 3.26156 light years. |
Source: engineeringtoolbox.com
Inch Metrification
The inch has been metrified: 1 inch is exactly 25.4 millimetres. This exact definition is the basis for the foot, yard, statute mile, and every inch-to-metric factor on this page, so inch-based conversions should be carried with enough significant figures before rounding final results.
Converters
Length Unit Converter
Inches to Millimetres
Feet to Metres
Miles to Kilometres
Interactive Conversion Charts
The original source images are linear conversion charts. Their data is restored here as interactive equivalents so each point can be inspected rather than only viewed as a static picture.
Miles to Kilometres Converter
Feet to Metres Converter
Inches to Millimetres Converter
Original Source Images
The following original source images are preserved to avoid losing visual reference material. When an image contains chart or tabular data, its extracted values are represented in the page tables, calculators, or interactive charts; remaining images are retained as visual source references.
Download and print Length Units Converter
Download and print Length Units Converter for offline use as a quick field reference.
Related Mobile Apps from The Engineering ToolBox
The original source includes a Related Mobile Apps section for Engineering ToolBox calculators and converters. The web equivalent is represented here by the online length calculator, restored conversion tables, interactive converter charts, and preserved printable source images.
Engineering Notes
- Exact inch definition: Since the international yard and pound agreement of 1959, the inch is defined as exactly 25.4 mm. This makes all inch-based conversions to metric exact when expressed with sufficient precision.
- Nautical mile: Originally defined as one minute of arc of latitude (1/60 of 1/360 of the Earth's circumference). Since 1929 the international nautical mile is fixed at exactly 1852 m. The US did not adopt this until 1954.
- Scandinavian mil: Used in Norway and Sweden, 1 mil = 10 000 metres (10 km). Not to be confused with the statute mile.
- Astronomical unit (AU): Used in planetary science, 1 AU ≈ 149 597 870 700 m (mean Earth–Sun distance, IAU 2012 definition).
- Standard reference temperature: Industrial length measurements are referenced to 20 °C (68 °F). Materials expand and contract with temperature, so measured lengths at other temperatures should be corrected.
- Cable length: A cable = 1/10 nautical mile = 185.2 m, used in naval and maritime contexts.