Length Converter

1 kilometer = 0.621371 miles. To convert km to miles: multiply by 0.621371. To convert miles to km: multiply by 1.60934. Quick mental math: km to miles — multiply by 0.6 (fast approximation). Miles to km — multiply by 1.6. Examples: 5 km = 3.107 miles. 10 km = 6.214 miles. 26.219 miles = 42.195 km (marathon). 100 km = 62.14 miles. Why different? The mile is defined as 1,609.344 meters. The US uses miles for road distances; most of the world uses kilometers. Most car speedometers in the US/UK show mph, international shows km/h.

1 meter = 3.28084 feet = 3 feet 3.37 inches. 1 foot = 0.3048 meters. 1 inch = 0.0254 meters. Common conversions: 1.8 m = 5 ft 10.9 in (≈ 5'11"). 1.7 m = 5 ft 6.9 in (≈ 5'7"). 2 m = 6 ft 6.7 in. 100 m = 328.084 ft. 1 mile = 5,280 ft = 1,609.344 m. Height conversions: for people (who care): 6'0" = 182.9 cm. 5'10" = 177.8 cm. 5'6" = 167.6 cm. 5'0" = 152.4 cm. Why two systems? The US, Liberia, and Myanmar are the only countries still primarily using imperial units. Most US scientific and medical work uses metric.

A nautical mile (nmi) = 1,852 meters = 1.15078 statute miles. It's defined as 1 minute of arc (1/60 of a degree) of latitude along any meridian. This makes nautical navigation straightforward: 60 nautical miles = 1 degree of latitude. A knot = 1 nautical mile per hour. Used in: aviation (international flights), maritime navigation, meteorology. Example: the Earth's circumference ≈ 21,600 nmi (360 degrees × 60 minutes). Distances between airports are typically given in nautical miles. A flight from New York to London is about 3,000 nmi.

1 inch = 2.54 centimeters (exact, by definition since 1959). 1 cm = 0.393701 inches. The inch was historically defined by various body measurements (thumb width, barleycorn length). Quick reference: 1 cm ≈ 0.4 inches. 2.5 cm ≈ 1 inch. 30 cm ≈ 1 foot. Common uses: cm for screen sizes in Europe, paper sizes (A4 = 21×29.7 cm), clothing measurements. Inches for US screen diagonal sizes (15" laptop), monitor sizes, TV sizes. A 15.6" laptop screen = 39.6 cm. A standard letter paper is 8.5×11 inches = 21.59×27.94 cm.

Smallest common: nanometer (nm) = 0.000000001 m. Used for: wavelength of light (400–700 nm visible spectrum), transistor sizes (3 nm in modern chips), DNA width (~2.5 nm). Ångström (Å) = 0.1 nm = 0.0000000001 m. Used in chemistry for atomic/molecular distances. Picometer (pm) = 0.000000000001 m. Atomic radii. Largest: parsec = 3.086×10¹⁶ meters = 3.26 light-years. Used in astronomy. Light-year = 9.461×10¹⁵ m. Astronomical unit (AU) = 1.496×10¹¹ m (Earth-Sun distance). Common useful: micrometer (μm) = 0.000001 m for biology cell sizes. Millimeter (mm) for precision machining.