Length Converter
Convert between metric and imperial measurements — instantly, privately, and with full floating-point precision.
What this converter handles
Length is one of the most frequently converted measurements — and one of the most error-prone when done manually. The gap between metric and imperial systems still causes real friction in construction, manufacturing, travel, and everyday life. This tool covers both systems comprehensively:
Metric
Nanometers, Micrometers, Millimeters, Centimeters, Meters, Kilometers
The global standard for science, engineering, and most of the world's road signage.
Imperial & US Customary
Inches, Feet, Yards, Miles, Nautical Miles
Dominant in the US, UK construction, and aviation/maritime contexts.
Who uses it — and why
Length conversion comes up in more contexts than most people expect — and the stakes vary significantly between them:
Architects & Construction Professionals
Working from blueprints that mix metric and imperial is common when collaborating across US and European teams. A beam specified at 3.65 meters needs to match a floor plan dimensioned in feet. Even a 0.5 cm discrepancy in a structural element can cascade into fitment problems on-site.
Travelers & Expats
Road signs, speed limits, and distances work differently depending on where you are. A US driver in Europe needs to quickly grasp that 100 km/h is about 62 mph — and that a destination listed as 45 km away is roughly 28 miles. Having a converter on hand removes the guesswork.
Fashion & Textile Professionals
Clothing patterns, fabric rolls, and sizing charts often exist in both centimeters and inches depending on country of origin. A pattern calling for 36 inches of fabric needs to be translated to about 91.4 cm when sourcing locally in a metric country.
Woodworkers & DIY Makers
Lumber in the US is sold in feet and inches; many imported tools and hardware are dimensioned in millimeters. If you're following a metric tutorial with imperial lumber, every measurement needs converting — and fractions of an inch matter when pieces need to fit flush.
Students & Educators
Physics and chemistry courses use SI units exclusively, but textbook problems sometimes draw on real-world data given in miles or feet. Quickly converting a problem's given values into meters keeps the calculation clean and avoids compounding errors.
Practical examples
A few common conversions with real-world context to help you sanity-check your results:
| Scenario | Input | Output |
|---|---|---|
| Average door height | 6 ft 8 in | 203.2 cm |
| Marathon distance | 26.2 miles | 42.195 km |
| A4 paper width | 210 mm | 8.27 in |
| Runway length | 3,000 m | 9,842.5 ft |
| Human hair thickness | 70 µm | 0.00276 in |
Tips for accurate results
Inches as decimals, not fractions
This tool uses decimal notation. If your measurement is 5¾ inches, enter it as 5.75. Fractions like ⅛ = 0.125, ¼ = 0.25, ½ = 0.5 — a quick mental conversion prevents errors.
Nautical miles are not statute miles
One nautical mile equals 1,852 meters (about 1.15 statute miles). They're used in aviation and maritime navigation and are based on one minute of arc of latitude — not an arbitrary historical unit.
Nanometers for microscale work
If you're working with semiconductor fabrication, optics, or biology, pay attention to scale. 1 micrometer = 1,000 nanometers. Confusing the two by a factor of 1,000 is a common mistake at this scale.
Feet-inches vs. decimal feet
In construction, 5 feet 6 inches and 5.5 decimal feet mean the same thing — but 5.6 decimal feet is actually 5 feet 7.2 inches. Always clarify which notation your plan uses before converting.
Quick reference — key conversion factors
These are the exact values the converter uses internally. Useful if you need to verify a result or do a back-of-envelope check:
Limitations to keep in mind
This tool converts units — it doesn't account for real-world measurement complexity:
- —Thermal expansion is not modeled. A steel beam that's 10 m at 20°C will be slightly longer at 80°C. For precision manufacturing, temperature corrections should be applied separately.
- —Survey feet differ from international feet by about 2 parts per million — negligible for most work, but relevant in large-scale geodetic surveys.
- —The tool works in Euclidean (flat) geometry. For geographic distances on Earth's curved surface, use a dedicated geodesy calculator.
- —Very large or very small values (e.g., light-years, Planck length) may hit floating-point precision limits in the browser.
Frequently asked questions
How many centimeters are in an inch?
Exactly 2.54 cm. This has been the internationally agreed definition since 1959, when the US, UK, and Commonwealth countries standardized the inch to eliminate the small discrepancy between their slightly different historical definitions.
What's the difference between a mile and a nautical mile?
A statute mile (the common road mile) is 1,609.344 meters. A nautical mile is 1,852 meters — about 15% longer. Nautical miles are used in aviation and maritime navigation because one nautical mile corresponds to one arcminute of latitude, which makes navigation calculations on charts much cleaner.
Why do the US and UK still use imperial measurements?
The UK officially adopted metric in the 1960s–70s for most official purposes, but imperial units persisted in daily life — particularly for road distances, pints, and human height. The US never formally metricated, though science, medicine, and the military use metric internally. Both systems will likely coexist for the foreseeable future.
Is 5 feet 10 inches the same as 5.10 feet?
No — this is a common mistake. 5 feet 10 inches = 5.833 decimal feet (since 10 ÷ 12 ≈ 0.833). The number after the decimal in decimal feet represents a fraction of a foot, not inches. When in doubt, convert feet-inches to total inches first, then to meters.
Is this conversion done on my device or sent to a server?
Everything runs locally in your browser. No values you type are sent anywhere — there's no backend, no API call, and nothing logged. The page works entirely with JavaScript running on your device.