Length Converter - Free Online Tool

Convert between length units like meters, feet, inches, miles, and kilometers. Free online length converter tool.

📏 Length Converter

Select your units from the lists below

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From Unit

Meter
Symbol: m

Kilometer
Symbol: km

Centimeter
Symbol: cm

Millimeter
Symbol: mm

Micrometer
Symbol: µm

Nanometer
Symbol: nm

Mile
Symbol: mi

Yard
Symbol: yd

Foot
Symbol: ft

Inch
Symbol: in

Nautical Mile
Symbol: nmi

Light Year
Symbol: ly

Astronomical Unit
Symbol: AU

To Unit

Meter
Symbol: m

Kilometer
Symbol: km

Centimeter
Symbol: cm

Millimeter
Symbol: mm

Micrometer
Symbol: µm

Nanometer
Symbol: nm

Mile
Symbol: mi

Yard
Symbol: yd

Foot
Symbol: ft

Inch
Symbol: in

Nautical Mile
Symbol: nmi

Light Year
Symbol: ly

Astronomical Unit
Symbol: AU

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📏 Length Converter

Length is one of the most basic measurements we use every day. Convert between meters, feet, inches, kilometers, miles, and dozens of other distance units instantly. Whether you're working on construction projects, scientific research, or planning a trip, our converter handles all the calculations for you.

📏 About Length

Length measures the distance between two points, making it one of the most basic physical quantities. In the International System of Units (SI), the meter serves as the standard unit for length. From architecture and engineering to navigation and manufacturing, accurate length measurements are used across countless fields. Different regions use different systems. The metric system (meters, kilometers, centimeters) dominates global science and most countries, while the imperial system (feet, inches, miles) remains common in the United States and a few other places. Being able to work with both systems and convert between them helps with international collaboration, trade, and everyday communication.

Understanding Length Measurement

Length is a measure of distance, representing the extent of something from end to end. In the International System of Quantities, length is a quantity with dimension distance, making it one of the seven base dimensions in physics. In most measurement systems, a base unit for length is chosen, from which all other length units are derived through multiplication or division. In the International System of Units (SI), the meter serves as the base unit for length. The modern definition of the meter, established in 1983 by the 17th General Conference on Weights and Measures, is based on the speed of light in vacuum—specifically, the distance light travels in 1/299,792,458 of a second. This definition ensures that length measurements are consistent and reproducible anywhere in the world, independent of physical artifacts that could change over time.

📜 History & Context

The history of length measurement dates back to the earliest human civilizations, when people needed to measure distances for construction, trade, and navigation. Ancient measurement systems often relied on human body parts as references, leading to units like the cubit (distance from elbow to fingertip), the foot, and the span (width of an outstretched hand). These body-based measurements varied significantly between individuals and regions, creating inconsistencies that complicated trade and communication. The need for standardization became critical as societies grew more complex. In ancient Egypt, standardized cubit rods were used, while the Romans developed a more systematic approach with units like the pes (foot) and mille passus (thousand paces, which became the mile). However, it wasn't until the French Revolution in the late 18th century that a truly universal system emerged. In 1790, the French Academy of Sciences proposed defining the meter as one ten-millionth of the distance from the North Pole to the Equator along the meridian passing through Paris. This ambitious project required surveying the meridian arc between Dunkirk and Barcelona, a task completed by Pierre Méchain and Jean-Baptiste Delambre between 1792 and 1798. The modern era of length measurement began with the Metre Convention of 1875, which established the International Bureau of Weights and Measures (BIPM) and created the first International Prototype Meter—a platinum-iridium bar. As science advanced, the definition evolved: in 1960, it was redefined using the wavelength of light from krypton-86, and in 1983, it was redefined based on the speed of light, making the meter a fundamental constant that can be reproduced anywhere in the universe.

✨ Fun Facts

• The original definition of the meter was based on measuring the Earth's meridian, but the actual prototype meter bar created in 1799 was about 0.2 millimeters shorter than intended due to measurement errors—yet it was kept as the standard.
• The inch was originally defined in medieval England as "three grains of barley, dry and round, placed end to end," while the yard has a legendary origin story involving King Henry I measuring from his nose to his outstretched thumb.
• Before standardization, the same unit name could mean different lengths in different cities or trades—a "foot" in one region might be noticeably different from a "foot" in another, making trade complicated.
• The modern meter is defined by the speed of light (299,792,458 meters per second), meaning that length is now tied to one of the most fundamental constants in physics.
• The furlong, still used in horse racing, comes from "furrow long"—the length of a furrow in a plowed field, standardized to 220 yards or one-eighth of a mile.

💡 Real-World Examples

• Construction projects rely on precise measurements: architects use meters and feet to design buildings, while contractors measure lumber, pipes, and wiring in both metric and imperial units depending on location.
• Navigation and mapping depend on accurate conversions: GPS systems use meters internally but often display distances in kilometers or miles based on user preference.
• Manufacturing industries use measurements for quality control: automotive parts must fit within precise tolerances measured in millimeters or thousandths of an inch.
• Scientific research requires precise measurements: physicists measure wavelengths in nanometers, astronomers use light-years for cosmic distances, and engineers work with everything from micrometers to kilometers.
• Sports and fitness track distances in various units: runners measure races in meters or kilometers, while American football fields are measured in yards.
• Textile and fashion industries measure fabric in yards, meters, or inches depending on the market, making conversions crucial for global supply chains.
• Surveying and land measurement use specialized units: surveyors work with chains (22 yards), rods, and acres, while modern GPS systems use meters.
• Everyday applications include measuring room dimensions in feet and inches, converting to meters for international furniture purchases, or understanding road signs that display distances in kilometers versus miles.

🔧 Common Applications

• Engineering and construction: Building dimensions, road lengths, and bridge spans need precise measurements. Projects often mix metric and imperial units depending on location and materials.
• Scientific research: Physicists work with nanometers for particle sizes, while astronomers use light-years for cosmic distances. Converting to more familiar units helps communicate findings.
• Manufacturing and quality control: Parts must fit together perfectly, which means working with precise measurements. Different industries and countries use different unit standards.
• Navigation and transportation: GPS systems, aviation, and maritime navigation all rely on accurate length measurements, converting between nautical miles, statute miles, kilometers, and meters as needed.
• Education and learning: Students and educators worldwide need to understand both metric and imperial systems, making conversion tools valuable for teaching and learning.

❓ Frequently Asked Questions

+ How do I convert meters to feet?

To convert meters to feet, multiply the meter value by 3.28084. For example, 1 meter equals 3.28084 feet, and 5 meters equals 16.4042 feet. This conversion factor comes from the definition of a foot as exactly 0.3048 meters.

+ What is the difference between a mile and a kilometer?

A mile is longer than a kilometer. One mile equals approximately 1.60934 kilometers, while one kilometer equals about 0.621371 miles. Miles are commonly used in the United States and United Kingdom, while kilometers are used in most other countries and in scientific contexts.

+ How many inches are in a foot?

There are exactly 12 inches in one foot. This is a standard conversion in the imperial system. For example, 2 feet equals 24 inches, and 0.5 feet equals 6 inches.

+ When should I use centimeters vs. inches?

Use centimeters when working with metric measurements, scientific calculations, or in countries that use the metric system. Use inches when working with imperial measurements, construction in the US, or when following US-based specifications. One inch equals 2.54 centimeters exactly.

+ How do I convert between metric and imperial length units?

To convert between metric and imperial units, use the conversion factors: 1 meter = 3.28084 feet, 1 kilometer = 0.621371 miles, 1 centimeter = 0.393701 inches, and 1 inch = 2.54 centimeters. Our converter handles all these calculations automatically for accurate results.