Length Converter

Length conversion is one of the most common measurement tasks in everyday life.

Whether you are shopping for furniture from an overseas retailer, checking your height in centimeters for a passport application, converting a building plan from feet to meters, or figuring out how far 10 kilometers actually is in miles, having a reliable length converter on hand saves time and prevents costly mistakes.

This tool converts between all standard length and distance units, including millimeters, centimeters, meters, kilometers, inches, feet, yards, miles, nautical miles, and more. Every conversion uses the exact factors defined by international metrology standards, so the results are precise enough for engineering, construction, and scientific work as well as everyday use.

The relationship between metric and imperial length units is straightforward once you know the key anchoring conversion: one inch equals exactly 25.4 millimeters. Every other length conversion between the two systems derives from this single defined relationship. Enter any value, select your units, and get an instant, accurate result without memorizing conversion tables or doing mental arithmetic.

How Length Units Relate to Each Other

All modern length measurements trace back to a single defined standard. The meter is the base unit of length in the International System of Units (SI). It was originally defined in 1793 as one ten-millionth of the distance from the equator to the North Pole, but since 1983 it has been defined as the distance light travels in vacuum in exactly 1/299,792,458 of a second. This gives the meter an absolute physical definition that does not change.

From the meter, all metric length units are derived using standard SI prefixes. One kilometer equals 1,000 meters. One centimeter equals one-hundredth of a meter (0.01 m). One millimeter equals one-thousandth of a meter (0.001 m). One micrometer equals one-millionth of a meter. The consistent decimal scaling is what makes the metric system so easy to work with internally.

Imperial and US customary length units have a more complex structure. The fundamental link between the two systems was established in 1959 when the international yard was defined as exactly 0.9144 meters. From this definition, one foot equals exactly 0.3048 meters and one inch equals exactly 25.4 millimeters. The mile is defined as 5,280 feet, which makes it exactly 1,609.344 meters.

Centimeters to Inches and Back

The centimeter-to-inch conversion is one of the most searched measurement conversions online, and for good reason. It comes up in clothing sizes, screen dimensions, paper sizes, and medical measurements.

The exact relationship: 1 inch = 2.54 centimeters. To convert centimeters to inches, divide by 2.54. To convert inches to centimeters, multiply by 2.54.

Common reference points:

• 1 cm = 0.3937 inches (roughly the width of a pencil)
• 10 cm = 3.937 inches (roughly the width of a softball)
• 30 cm = 11.81 inches (roughly the length of a standard ruler)
• 100 cm = 39.37 inches (1 meter, roughly the height of a kitchen counter)

Screen sizes are measured diagonally in inches worldwide, even in metric countries. A 27-inch monitor has a diagonal of 68.58 cm. A 6.7-inch phone screen is 17.02 cm diagonally.

Paper sizes illustrate the metric-imperial divide clearly. US Letter paper is 8.5 x 11 inches (21.59 x 27.94 cm). The international A4 standard is 210 x 297 mm (8.27 x 11.69 inches). A4 is slightly narrower and taller than Letter.

Feet to Meters Conversion

Feet-to-meters conversion is essential in construction, real estate, aviation, and sports.

The exact relationship: 1 foot = 0.3048 meters (exactly). To convert feet to meters, multiply by 0.3048. To convert meters to feet, divide by 0.3048 (or multiply by 3.2808).

Height conversions are among the most common applications. Here are reference points:

• 5 feet = 1.524 meters
• 5 feet 6 inches = 1.676 meters
• 6 feet = 1.829 meters
• 6 feet 2 inches = 1.880 meters

Real estate measurements differ by country. A 1,500-square-foot apartment is approximately 139 square meters. A 2,500-square-foot house is approximately 232 square meters. When comparing international property listings, getting the area conversion right can mean the difference between a spacious flat and a closet.

Aviation uses feet for altitude worldwide, even in countries that otherwise use metric. Cruising altitude of 35,000 feet equals 10,668 meters or approximately 10.7 kilometers. This is one of the few areas where the entire world has standardized on an imperial unit.

Miles to Kilometers

The mile-to-kilometer conversion is essential for travelers, runners, and anyone comparing distances across countries.

The exact relationship: 1 mile = 1.609344 kilometers. For quick mental math, multiply miles by 1.6 or divide kilometers by 1.6.

A useful trick: The Fibonacci sequence (1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89…) roughly approximates the mile-to-kilometer conversion. Each number in the sequence, when converted from miles, is approximately the next number in kilometers. Five miles is roughly 8 kilometers. Eight miles is roughly 13 kilometers. Thirteen miles is roughly 21 kilometers. This works because the ratio between consecutive Fibonacci numbers approaches the golden ratio (1.618), which is close to the miles-to-kilometers factor (1.609).

Running distances:

• 5K = 3.107 miles
• 10K = 6.214 miles
• Half marathon (13.1 miles) = 21.1 kilometers
• Marathon (26.2 miles) = 42.2 kilometers

Driving distances: When traveling between countries with different systems, knowing that 100 km/h equals about 62 mph and 60 mph equals about 97 km/h helps you judge speed limits at a glance.

Specialized Length Units

Beyond the standard metric and imperial units, several specialized length units are still in active use.

Nautical Miles. One nautical mile equals exactly 1,852 meters or approximately 1.151 statute miles. It is defined as one minute of arc of latitude along any meridian. This makes nautical miles inherently useful for navigation because they relate directly to the coordinate system used on charts. Maritime and aviation speed is measured in knots, where one knot equals one nautical mile per hour.

Micrometers and Nanometers. At the small end of the scale, micrometers (also called microns) and nanometers are used in manufacturing, biology, and semiconductor technology. A human hair is roughly 70 micrometers in diameter. Semiconductor transistors in modern processors are measured in nanometers, with current technology reaching 3 to 5 nanometers. One micrometer equals 1,000 nanometers.

Light-Years and Astronomical Units. At the large end, astronomical distances use their own units. One astronomical unit (AU) is the average Earth-to-Sun distance, approximately 149.6 million kilometers. One light-year is the distance light travels in one year, approximately 9.461 trillion kilometers. The nearest star to our Sun, Proxima Centauri, is about 4.24 light-years away.

Fathoms. A fathom equals 6 feet (1.8288 meters) and is traditionally used for measuring water depth. The term comes from the Old English word for the span of outstretched arms, which averages about 6 feet.

Practical Tips for Length Conversion

Carry a mental toolkit of reference conversions. You do not need to memorize exact factors if you know a few reference points. Knowing that 1 meter is about 3 feet 3 inches, 1 kilometer is about 0.6 miles, and 1 inch is about 2.5 cm covers most everyday situations.

Be careful with squared and cubed units. When converting area or volume, you must square or cube the linear conversion factor. One square meter does not equal 3.28 square feet; it equals 10.76 square feet (3.2808 squared). One cubic meter equals 35.31 cubic feet (3.2808 cubed). This is a common source of error.

Distinguish between survey feet and international feet. In the United States, the "survey foot" (1 foot = 1200/3937 meters) was historically used for land surveying and differs slightly from the international foot (1 foot = 0.3048 meters exactly). The difference is only about 2 parts per million, but over large distances it accumulates. The US officially retired the survey foot on January 1, 2023, in favor of the international foot.

Check your unit labels. Millimeters (mm), centimeters (cm), and meters (m) can be easily confused in technical drawings and specifications. A dimension listed as 25 when it should be 250 is a ten-to-one error that can ruin a project. Always verify the unit of measurement, not just the number.

For broader measurement conversions beyond length, use the Unit Converter. For weight-specific conversions, try the Weight Converter.

Frequently Asked Questions

How many centimeters are in an inch?

One inch equals exactly 2.54 centimeters. This is a defined conversion, not an approximation. To convert inches to centimeters, multiply by 2.54. To convert centimeters to inches, divide by 2.54 or multiply by 0.3937.

How do I convert feet and inches to centimeters?

First convert the entire measurement to inches (multiply feet by 12, then add the remaining inches). Then multiply the total inches by 2.54 to get centimeters. For example, 5 feet 8 inches = 68 inches = 68 x 2.54 = 172.72 cm.

How many kilometers are in a mile?

One mile equals exactly 1.609344 kilometers. For a quick estimate, multiply miles by 1.6. To convert kilometers to miles, multiply by 0.6214 or divide by 1.609.

What is the difference between a nautical mile and a regular mile?

A nautical mile equals 1,852 meters or about 1.151 statute (regular) miles. Nautical miles are based on the Earth’s geometry, with one nautical mile equaling one minute of latitude. They are used in maritime and aviation navigation.

How tall is 180 cm in feet and inches?

180 cm equals approximately 5 feet 10.87 inches, commonly rounded to 5 feet 11 inches. To calculate: divide 180 by 2.54 to get 70.87 inches, then divide by 12 to get 5 feet with 10.87 inches remaining.

What is a micrometer?

A micrometer (also called a micron) is one-millionth of a meter, or one-thousandth of a millimeter. It is used to measure very small objects such as bacteria (typically 1 to 10 micrometers), human hair diameter (about 70 micrometers), and semiconductor components.

Why does the US still use feet and inches?

The US has not formally adopted the metric system for everyday use, despite Congress authorizing it in 1975. The cost of changing infrastructure, road signs, manufacturing standards, and ingrained cultural habits has prevented a full transition. However, US science, medicine, and military operations use metric extensively.

Conversion factors based on NIST and BIPM international standards. Data accurate as of: March 2026