Length Converter

One inch equals exactly 2.54 centimeters, by international definition since 1959. This is an exact value, not an approximation. To convert inches to cm, multiply by 2.54. To convert cm to inches, divide by 2.54 (or multiply by 0.393701). Example: 6 inches = 15.24 cm. 30 cm = 11.811 inches.

One meter equals exactly 3.28084 feet (or more precisely 100/30.48 feet). One foot equals exactly 0.3048 meters. These are exact values by international agreement. Common conversions: 5 feet = 1.524 m · 6 feet = 1.8288 m · 1.80 m = 5 feet 10.87 inches. For height conversion, use feet and inches separately.

One international mile equals exactly 1.609344 kilometers. Conversely, 1 km = 0.621371 miles. Common running distances: 5 km = 3.107 miles · 10 km = 6.214 miles · 21.097 km (half marathon) = 13.109 miles · 42.195 km (marathon) = 26.219 miles. Speed signs in the UK show mph; in mainland Europe they show km/h.

There are exactly 12 inches in one foot. The foot is divided into 12 inches, and each inch is divided into fractions (typically halves, quarters, eighths and sixteenths in construction). Other imperial length relationships: 3 feet = 1 yard · 5,280 feet = 1 mile · 1,760 yards = 1 mile. One foot = 30.48 cm = 0.3048 m.

Divide centimeters by 30.48 to get total feet as a decimal. Subtract the whole number of feet to get the fractional part, then multiply by 12 to get inches. Example: 175 cm ÷ 30.48 = 5.7415 feet = 5 feet 8.9 inches. Common heights: 160 cm = 5’3” · 170 cm = 5’7” · 180 cm = 5’11” · 190 cm = 6’3”.

A nautical mile equals 1,852 meters (1.852 km), which is approximately 1.151 international miles. It is defined as one minute of arc of latitude along a meridian of the Earth. Nautical miles are used in aviation and maritime navigation because they correspond directly to degrees of latitude. One knot = one nautical mile per hour.

One inch equals exactly 25.4 millimeters (since 1 inch = 2.54 cm = 25.4 mm). This is the standard used in engineering and manufacturing. Common conversions: 10 mm = 0.3937 in · 25 mm = 0.984 in · 100 mm = 3.937 in. Wrench and bolt sizes are measured in mm (metric) or fractions of inches (imperial), which is why both systems still coexist in manufacturing.

One light year is approximately 9.461 × 10¹&sup5; meters (9.461 trillion km or about 5.879 trillion miles). It is the distance light travels in a vacuum in one Julian year (365.25 days). The nearest star system, Alpha Centauri, is about 4.37 light years away. Light years are used only for astronomical distances — they are not practical for everyday measurement.

One yard equals exactly 0.9144 meters, so a meter is slightly longer than a yard (by about 9.36 cm or 3.68 inches). One yard = 3 feet = 36 inches. Yards are used in American football (field = 100 yards), fabric measurement in the US/UK, and golf (distances to the hole). Meters are used for the same purposes in most of the rest of the world.

A quick mental trick: multiply miles by 1.6 to get an approximate km value. For better accuracy, multiply by 8 then divide by 5. Example: 60 miles × 1.6 = 96 km (exact: 96.56 km). Going the other way, multiply km by 0.6 to get approximate miles. The Fibonacci sequence also works: consecutive Fibonacci numbers (5, 8, 13, 21, 34...) approximate the miles-to-km ratio.