Length Unit Converter

Convert between units of length and distance.

Supported Units

• Kilometer (km): The kilometer is equal to 1,000 meters and is the standard unit for expressing distances between cities, road signs, and geographic measurements in most countries. It was introduced as part of the metric system during the French Revolution. A marathon race covers 42.195 kilometers, and most countries outside the United States use kilometers for speed limits and road distances. In scientific contexts, it is used for planetary distances and the sizes of geographic features.
• Meter (m): The meter is the base unit of length in the International System of Units (SI). Originally defined in 1793 as one ten-millionth of the distance from the equator to the North Pole, it is now defined by the speed of light in vacuum as the distance light travels in 1/299,792,458 of a second. The meter is used worldwide for everyday measurements such as room dimensions, human height, and architectural plans. It serves as the foundation for all other metric length units.
• Centimeter (cm): The centimeter is one-hundredth of a meter and is commonly used for everyday small-scale measurements. In many countries, human height is expressed in centimeters rather than feet and inches. Rulers and tape measures are typically graduated in centimeters, making it the go-to unit for crafting, sewing, and carpentry. In medicine, tumor sizes, wound dimensions, and other anatomical measurements are recorded in centimeters.
• Millimeter (mm): The millimeter is one-thousandth of a meter and is used wherever high precision is required. Engineers specify screw sizes, circuit board dimensions, and mechanical tolerances in millimeters. In meteorology, rainfall is measured in millimeters, with weather reports stating amounts like "20 mm of rain expected today." Paper thickness, smartphone dimensions, and dental measurements are also commonly expressed in millimeters.
• Micrometer (µm): The micrometer, formerly known as the micron, is one-millionth of a meter or one-thousandth of a millimeter. It is essential in biology for describing cell sizes—a red blood cell is about 7 µm in diameter, and typical bacteria measure around 1 to 5 µm. In semiconductor manufacturing, transistor gate lengths and circuit features are measured in micrometers or smaller. Optical fiber core diameters, thin-film coatings, and particle sizes in air-quality studies are also expressed in micrometers.
• Mile (mi): The mile is a unit of length in the imperial and US customary systems, defined as exactly 1,609.344 meters. Its origin traces back to the Roman "mille passus," meaning one thousand paces. In the United States and the United Kingdom, road distances and speed limits are posted in miles, and car odometers display mileage. The mile is also central to airline frequent-flyer programs, where travel distances are tracked and rewarded in miles.
• Yard (yd): The yard is a unit of length in the imperial and US customary systems, defined as exactly 0.9144 meters. One popular legend suggests it originated as the distance from King Henry I's nose to his outstretched thumb. American football fields are 100 yards long, and golf courses measure distances in yards. In the United States and United Kingdom, fabric is sometimes sold by the yard, and garden or property dimensions may also be expressed in yards.
• Foot (ft): The foot is a unit of length in the imperial and US customary systems, equal to exactly 0.3048 meters or 12 inches. Its name comes from the length of a human foot, and it has been used as a measure since ancient civilizations. In the United States, height is commonly expressed in feet and inches (for example, "5 feet 10 inches"), and real estate listings use square feet for floor area. In aviation worldwide, altitude is measured in feet, regardless of whether the country otherwise uses the metric system.
• Inch (in): The inch is a unit of length in the imperial and US customary systems, defined as exactly 25.4 millimeters. The word comes from the Latin "uncia," meaning one-twelfth, as there are 12 inches in a foot. Screen sizes for televisions, monitors, and smartphones are universally measured diagonally in inches. In plumbing and hardware, pipe diameters and bolt sizes are often specified in inches, even in countries that otherwise use the metric system.
• Nautical Mile (nmi): The nautical mile is a unit of distance used in maritime and air navigation, defined as exactly 1,852 meters. It was originally based on one minute of arc of latitude along any meridian of the Earth, making it naturally suited for navigation on charts. The knot, a unit of speed equal to one nautical mile per hour, is derived from this unit. Nautical miles are used internationally for charting sea and air routes, and they remain the standard in maritime law and international treaties governing territorial waters.

How to Use

1. Select the unit you want to convert from in the "From" dropdown.

2. Select the unit you want to convert to in the "To" dropdown.

3. Enter a value and the result will be displayed in real time.

4. Use the swap button to reverse the conversion direction.