Instantly convert feet, meters, inches, miles, kilometers, and 15+ more units. Includes height converter and real-world size references.
The United States is one of only three countries that hasn't officially adopted the metric system, creating constant conversion needs. Americans encounter metric measurements in science, medicine, international recipes, and imported products daily. In construction, US residential building uses imperial measurements while engineering specifications and most global building codes use metric. A 2×4 stud is actually 1.5 inches × 3.5 inches, 38mm × 89mm in metric. Knowing these conversions prevents costly material errors. Most useful conversions to know intuitively: 1 inch = 2.54 cm (exact), 1 foot = 30.48 cm, 1 meter ≈ 3 feet 3 inches, 1 mile = 1.609 km, 1 km ≈ 0.621 miles. For quick km-to-miles mental math: multiply km by 0.6 for a close estimate.
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 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 |
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 |
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.
| 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 |
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).
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.
Both imperial and metric scales on one tape, no conversion needed in the field.
View on Amazon →Instant measurements in any unit, metric or imperial, at the press of a button.
View on Amazon →Quick-reference card for all common length, weight, and volume conversions.
View on Amazon →