Understanding Length Conversions
Every length conversion relies on one concept: a shared base unit. This guide covers the math behind every unit in our converter, the history of how these units were defined, and the practical contexts where each one matters.
How Length Conversion Works
All units in this converter share a common reference: the meter. To convert from any unit to any other, the value is first expressed in meters (the base), then divided by the target unit's meter-equivalent. The general formula is:
Result = Value × (source unit in meters) ÷ (target unit in meters)
For example, converting 5 miles to kilometers: 5 × 1,609.34 ÷ 1,000 = 8.04672 km. The meter factors cancel out, leaving a clean ratio between the two units.
Conversion Factors: Every Unit Explained
Below is the exact relationship of each unit to one meter — the factor our converter uses internally.
Meter (m)
Factor: 1 (base unit)
The meter is the SI base unit of length. Since 2019, it has been defined as the distance light travels in a vacuum in exactly 1/299,792,458 of a second. Before that, it was based on a platinum-iridium bar stored in Paris, and originally on one ten-millionth of the distance from the equator to the North Pole.
Kilometer (km)
Factor: 1 km = 1,000 m
The prefix "kilo" means 1,000. Kilometers are the standard unit for road distances, geographic measurements, and travel in most countries. A marathon is 42.195 km. To convert km to meters, multiply by 1,000; to go the other way, divide.
Centimeter (cm)
Factor: 1 cm = 0.01 m
One hundredth of a meter. Centimeters are the go-to unit for body measurements, clothing sizes, and screen dimensions in metric countries. There are 2.54 cm in one inch — an exact value established by international agreement in 1959.
Millimeter (mm)
Factor: 1 mm = 0.001 m
One thousandth of a meter. Millimeters are used in engineering, manufacturing, and precision work. Rainfall is reported in millimeters, and most mechanical tolerances in technical drawings are specified in mm. There are 25.4 mm per inch.
Mile (mi)
Factor: 1 mi = 1,609.34 m
The statute mile is the standard unit for road distances in the US, UK, and a handful of other countries. It equals 5,280 feet or 1,760 yards. The word "mile" derives from the Latin mille passus (a thousand paces), the Roman unit of roughly 4,850 feet.
Yard (yd)
Factor: 1 yd = 0.9144 m
Three feet or 36 inches. The yard is used in American football (field length: 100 yards), fabric measurement, and golf. It was standardized internationally in 1959 as exactly 0.9144 meters, ending centuries of slightly different national definitions.
Foot (ft)
Factor: 1 ft = 0.3048 m
Twelve inches. The foot is the primary unit for height (people), altitude (aviation), and real estate (square footage) in the United States. One foot equals exactly 30.48 centimeters. Historically, the foot was literally based on the length of a human foot, though whose foot varied by era and region.
Inch (in)
Factor: 1 in = 0.0254 m
The smallest imperial unit in common use. One inch equals exactly 25.4 millimeters. Inches are used for screen sizes (measured diagonally), tire widths, and pipe diameters. The inch is believed to have been originally defined as the width of a man's thumb.
Common Length Conversions at a Glance
Quick reference for the conversions people search for most frequently.
| From | To | Formula | Example |
|---|---|---|---|
| Meters | Feet | m × 3.28084 | 10 m = 32.81 ft |
| Feet | Meters | ft × 0.3048 | 6 ft = 1.83 m |
| Miles | Kilometers | mi × 1.60934 | 26.2 mi = 42.16 km |
| Kilometers | Miles | km × 0.621371 | 100 km = 62.14 mi |
| Inches | Centimeters | in × 2.54 | 12 in = 30.48 cm |
| Yards | Meters | yd × 0.9144 | 100 yd = 91.44 m |
Metric vs. Imperial: A Brief History
The metric system was created during the French Revolution in the 1790s as a rational, decimal-based alternative to the hundreds of inconsistent local units used across Europe. It was designed so that every prefix represents a power of 10 — milli (1/1,000), centi (1/100), kilo (1,000) — making unit conversion a matter of moving the decimal point.
The imperial system evolved organically from Roman, Anglo-Saxon, and medieval English measurements. Its relationships are irregular — 12 inches in a foot, 3 feet in a yard, 5,280 feet in a mile — because each unit was defined independently for a specific trade or context, not as part of a unified system.
Today, the metric system is the official standard in every country except the United States, Myanmar, and Liberia. Even the US defines its imperial units in terms of metric equivalents: one inch is legally defined as exactly 25.4 millimeters.
Length Conversion FAQ
? How many feet are in a meter?
One meter equals approximately 3.28084 feet. To convert meters to feet, multiply the meter value by 3.28084. For example, 5 meters = 16.4042 feet.
? How many miles are in a kilometer?
One kilometer equals approximately 0.621371 miles. Conversely, one mile equals 1.60934 kilometers. The mile is used primarily in the United States and United Kingdom, while the kilometer is the global standard.
? How do you convert inches to centimeters?
Multiply the number of inches by 2.54 to get centimeters. This is an exact conversion — one inch is defined as exactly 2.54 centimeters since the international yard agreement of 1959.
? What is the difference between metric and imperial length units?
Metric units (meters, kilometers, centimeters, millimeters) are based on powers of 10, making conversions straightforward. Imperial units (miles, yards, feet, inches) use irregular ratios: 12 inches per foot, 3 feet per yard, 1,760 yards per mile. The metric system is used by most countries; the US, Liberia, and Myanmar still primarily use imperial.