Length Converter
Convert between millimetres, centimetres, metres, kilometres, inches, feet, yards, and miles with precise conversion factors shown.
Length Converter
Enter a value in any unit β see the conversion in all others instantly. All calculations run in your browser.
Quick References
How to Convert Between Metric and Imperial Length Units
You just received a supplier quote for a steel bracket in millimeters, but your CAD drawing is in inches. Typing the wrong conversion into a purchase order can cost hundreds of dollars in rework. Enter your value, pick the source unit from the dropdown, and every other length unit updates instantly β no need to hit a calculate button or wait for a page refresh. The copy-to-clipboard button on each result means you can paste the converted value straight into your spreadsheet or email.
The converter covers 11 units spanning nanometers to kilometers and inches to nautical miles. Whether you are matching a pipe fitting spec in millimeters to a catalogue listing in inches, or comparing a hiking trail measured in miles against a fitness tracker reporting kilometers, the tool gives you every equivalent at a glance. The quick-reference strip at the bottom translates the current value into familiar objects β a credit card, a smartphone, a football pitch β so you can sanity-check whether the number makes intuitive sense before using it.
When you need quick imperial-to-metric swaps for procurement
A procurement officer at a US manufacturer orders a 25 mm bearing from a German supplier. The internal spec sheet lists the clearance as 0.010 inches. Converting 0.010 in to mm gives 0.254 mm β a critical tolerance that determines whether the bearing fits. Getting this wrong means a delayed production line. The tool shows the conversion instantly, and the copy button eliminates transcription errors between the converter and the purchase order.
A British expat comparing London flats listed in square feet against Sydney apartments listed in square metres needs a quick length sanity check: a room described as 12 ft wide converts to 3.6576 m. That is narrower than the 4 m rooms they are used to. When your estate agent says the garden is 150 ft deep, converting to metres (45.72 m) helps you visualise the actual space without a tape measure.
A marathon runner training for the London Marathon knows the race is 26.2 miles, but their GPS watch displays distance in kilometres. Converting 26.2 mi to km gives 42.1648 km β matching the official 42.195 km course (the small difference accounts for the measured certified distance). Cyclists planning a century ride (100 mi) can instantly see that equals 160.934 km, helping them set realistic training targets.
How the Length Converter Calculates Exact Conversions
Every length unit in the converter is stored as a fixed number of meters. When you type 5 inches, the tool multiplies 5 by 0.0254 (the exact meter value of one inch) to get 0.127 m, then divides by the target unit's factor to produce the result. Because every conversion passes through meters in a single step, there is no chain of intermediate conversions that could introduce rounding drift. The result for 5 inches to centimeters is exactly 12.7 cm β not an approximation rounded at an intermediate stage.
Why imperial-to-metric factors are exact (not rounded)
In 1959, six English-speaking nations signed the International Yard and Pound Agreement, defining the inch as exactly 25.4 millimeters. That single definition cascades: 1 foot becomes exactly 0.3048 m, 1 yard exactly 0.9144 m, and 1 mile exactly 1609.344 m. These are not rounded approximations β they are exact rational numbers. The nautical mile was defined independently in 1929 as exactly 1852 m. Because the factors are exact, converting 1 mile to feet gives exactly 5280, not 5279.9999.
For metric units, the factors are powers of ten by definition: 1 mm = 0.001 m, 1 cm = 0.01 m, 1 km = 1000 m. Converting between two metric units (say, millimeters to kilometers) simply shifts the decimal point β no floating-point arithmetic is needed at all for these cases. The only time IEEE 754 rounding can appear is when converting between metric and imperial, and even then it only affects digits beyond the 15th significant figure.
How the display adapts to very large and very small numbers
A length of 0.000000001 meters (1 nanometer) is meaningful in semiconductor manufacturing β Intel's current process nodes are below 5 nm. Converting that to kilometers gives 0.000000000000001 km, which is unreadable in fixed notation. The tool switches to scientific notation (1 Γ 10β»ΒΉΒ² km) for any result below 0.001. Conversely, the distance from Earth to the Moon is about 384,400,000 m. Displaying that in inches yields roughly 15,133,858,267,716.5 inches, which the tool formats with locale separators and two decimal places for readability.
The formatting thresholds are: values below 0.001 and above 1 billion use scientific notation; values between 1,000 and 1 billion use locale-formatted numbers with 2-4 decimal places; values between 0.001 and 1,000 use 6-8 decimal places. This keeps the output scannable whether you are measuring transistor features or interplanetary distances.
Frequently Asked Questions
How many centimeters are in 5 inches?
Five inches equals exactly 12.7 centimeters. The conversion factor is exact: 1 inch = 2.54 cm, established by international agreement in 1959. This is not an approximation β it is a precise rational number used in manufacturing, machining, and engineering worldwide. For quick mental estimates, each inch is about 2.5 cm, so multiply the inch value by 2.5 for a ballpark figure.
Why does this tool show different results than Google's built-in converter?
Google's converter uses the same exact conversion factors, so results should match to 15+ significant digits. If you see a difference, it is likely due to display rounding β Google might round 1.60934 km/mi to 1.61, while this tool shows more decimal places. For practical purposes (cooking, fitness, construction), the results are identical. The difference only matters in scientific or engineering contexts requiring extreme precision.
What is a nautical mile and why is it different from a regular mile?
A nautical mile equals exactly 1852 meters, while a regular (statute) mile is 1609.344 meters. The nautical mile was designed for navigation: it equals one minute of latitude along the Earth's meridian. This means a navigator can measure the distance between two latitude lines on a chart and know the nautical distance directly. Speed at sea is measured in knots (nautical miles per hour), and aviation uses nautical miles for the same reason β it aligns with the coordinate system used on navigation charts.
Can I use this for construction material estimates?
Yes. If your lumber supplier sells boards measured in feet but your project plans are in meters, enter the foot measurement and the meter equivalent appears instantly. For example, a 10 ft board is exactly 3.048 m. Flooring, tiling, and drywall estimates all benefit from quick unit swaps, especially when sourcing materials internationally or following plans from a different country's standards.
Why does converting 1 mile to feet give exactly 5280?
The mile-to-foot relationship is exact by definition: 1 mile = 5280 feet. This comes from the chain of exact definitions: 1 mile = 8 furlongs, 1 furlong = 660 feet, and 8 Γ 660 = 5280. Since 1959, the foot has been defined as exactly 0.3048 meters, and the mile as exactly 1609.344 meters. Dividing 1609.344 by 0.3048 gives exactly 5280 β no rounding involved.
How do I convert kilometers to miles for a road trip?
Divide the kilometer value by 1.609344. For example, a 300 km drive equals approximately 186.41 miles. A quick mental shortcut: 100 km is roughly 62.1 miles, so multiply the km value by 0.621 for a ballpark figure. This tool gives the precise result, but the 0.621 rule of thumb is accurate to within about 0.1% for quick planning.