Length Converter
Instantly convert feet, meters, inches, miles, kilometers, and 15+ more units. Includes height converter and real-world size references.
Length Units: Metric vs. Imperial
The world uses two primary measurement systems for length. The metric system (International System of Units, SI) is used by almost every country on Earth and is based on powers of 10 — making conversions as simple as moving a decimal point. The imperial system is used primarily in the United States, with historical use in the UK, and is based on seemingly arbitrary historical units derived from body parts and agricultural measures.
The Metric System
The meter is the base unit of length in the metric system, defined since 1983 as the distance light travels in a vacuum in 1/299,792,458 of a second. All metric length units are derived by multiplying or dividing by powers of 10:
| Unit | Symbol | Meters | Common use |
|---|
| Kilometer | km | 1,000 m | Road distances, geography |
| Meter | m | 1 m | Room dimensions, height, fabric |
| Centimeter | cm | 0.01 m | Human height, clothing sizes |
| Millimeter | mm | 0.001 m | Engineering, rainfall, small objects |
| Micrometer | μm | 0.000001 m | Bacteria, human hair diameter |
| Nanometer | nm | 0.000000001 m | Wavelengths of light, transistors |
The Imperial System
Imperial units are defined precisely in terms of metric equivalents. The inch is defined as exactly 2.54 centimeters (since 1959). The foot is 12 inches (0.3048 m). The yard is 3 feet (0.9144 m). The mile is 5,280 feet (1,609.344 m exactly) — a number that arose from the Roman mile of 1,000 double paces combined with English agricultural furlongs.
| Unit | Symbol | In meters | Common use |
|---|
| Mile | mi | 1,609.344 m | Road distances in US/UK |
| Yard | yd | 0.9144 m | Football fields, fabric |
| Foot | ft | 0.3048 m | Height (US), altitude, room size |
| Inch | in | 0.0254 m | Screen sizes, pipe diameter, rainfall |
| Nautical Mile | nmi | 1,852 m | Navigation, aviation, maritime |
Most Important Conversions to Know
A few conversions are worth memorizing because they come up constantly in everyday life. The most useful: 1 inch = 2.54 cm (exact, by definition). 1 foot = 30.48 cm. 1 mile ≈ 1.609 km (or roughly 8 km = 5 miles as a quick mental estimate). 1 meter ≈ 3.281 feet (or roughly 3 feet 3 inches). For height conversions, 5 feet = 152.4 cm, 6 feet = 182.88 cm.
💡 Quick Mental Tricks: Miles to km: multiply by 1.6 (or by 8 then divide by 5). Km to miles: multiply by 0.6. Inches to cm: multiply by 2.5 (close enough for most purposes). Cm to inches: divide by 2.5. Feet to meters: divide by 3.3. Meters to feet: multiply by 3.3.
Height Conversions: Feet/Inches to Centimeters
| Height (ft/in) | Centimeters | Meters | Context |
|---|
| 5'0" | 152.4 cm | 1.524 m | Average female height (US) |
| 5'4" | 162.6 cm | 1.626 m | Average female height (US) |
| 5'7" | 170.2 cm | 1.702 m | Average male height (global) |
| 5'9" | 175.3 cm | 1.753 m | Average male height (US) |
| 6'0" | 182.9 cm | 1.829 m | Considered "tall" in most countries |
| 6'6" | 198.1 cm | 1.981 m | NBA average height |
Nautical Miles and Aviation
The nautical mile (1,852 m) is based on one arc-minute of latitude on Earth’s surface, making it especially useful for navigation. A knot is one nautical mile per hour. Flight distances, maritime distances, and weather reporting all use nautical miles. For reference, the circumference of Earth is 21,600 nautical miles (360 degrees × 60 arc-minutes per degree).
Astronomical Distances
Beyond everyday measurements, scientists use specialized units for space. An Astronomical Unit (AU) is the average Earth–Sun distance: 149,597,870.7 km. A light-year is the distance light travels in one year: 9.461 × 10¹⁵ meters. A parsec (used in professional astronomy) is 3.262 light-years or 206,265 AU. The nearest star, Proxima Centauri, is 4.24 light-years away.
Frequently Asked Questions
How do I convert feet to meters?
Multiply feet by 0.3048. This is exact — 1 foot is defined as exactly 0.3048 meters. For a quick mental estimate, divide by 3.3 (close enough for most purposes). Examples: 5 feet = 1.524 m, 6 feet = 1.8288 m, 10 feet = 3.048 m, 100 feet = 30.48 m.
How many centimeters are in an inch?
Exactly 2.54 centimeters. This is not an approximation — it’s the official international definition established in 1959. To convert inches to cm, multiply by 2.54. To go the other direction, divide by 2.54 (or multiply by 0.3937). Example: 12 inches = 30.48 cm. 24 inches = 60.96 cm. 1 foot (12 inches) = 30.48 cm exactly.
How do I convert miles to kilometers?
Multiply miles by 1.60934. The exact value is 1.609344 km per mile. For a quick estimate, multiply by 1.6 — you’ll be within 0.2%. The easy mental trick: 5 miles = 8 km exactly (well, 8.047 km). So multiply miles by 8 then divide by 5. Example: 26.2 miles (marathon) = 42.195 km. 100 miles = 160.93 km.
How do I convert my height from feet and inches to centimeters?
Use the Height Converter tab above for instant results. The formula: multiply feet by 30.48 and inches by 2.54, then add them together. Example for 5’10”: (5 × 30.48) + (10 × 2.54) = 152.4 + 25.4 = 177.8 cm. For cm to feet/inches: divide cm by 2.54 to get total inches, then divide by 12 for feet and the remainder is inches.
What is a nautical mile and how does it differ from a regular mile?
A nautical mile (1,852 meters) is longer than a statute (land) mile (1,609.344 meters) — about 15% longer. It’s defined as one arc-minute of latitude, making it ideal for navigation since one degree of latitude = 60 nautical miles anywhere on Earth. Aviation and maritime navigation use nautical miles; speed is measured in knots (nautical miles per hour). A regular mile is used for road distances in the US and UK.
Why does the US still use feet and inches instead of metric?
The US is one of only three countries (with Liberia and Myanmar) that hasn’t officially adopted the metric system. Metrication efforts in the 1970s stalled due to costs and public resistance. Despite this, the US uses metric in science, medicine, nutrition labeling, and military/technical contexts. The imperial units persist primarily in everyday consumer contexts: height, road distances, temperatures in Fahrenheit, and building dimensions.
How small is a nanometer?
One nanometer (nm) is one billionth of a meter (10⁻⁹ m). A human hair is roughly 80,000–100,000 nm wide. Visible light wavelengths span 380–700 nm. Modern computer processor transistors are measured in nanometers — current cutting-edge chips use 3–5 nm process nodes. A water molecule is about 0.275 nm in diameter. At this scale, quantum mechanical effects dominate and classical physics breaks down.