Length Conversion: cm, Inches, Feet, Meters Explained
Length conversion is one of the most common everyday unit conversion needs. Whether you are figuring out your height in centimeters for a European form, converting a recipe pan size from inches to centimeters, calculating how long a 5-mile commute is in kilometers, or reading a technical drawing that uses millimeters instead of inches, you need a reliable reference. This guide covers all major length units with exact conversion factors, practical examples, and formulas you can use anywhere.
The Length Units You Need to Know
Length units fall into two main systems: metric (SI) and imperial/US customary. Metric length units, from smallest to largest: Millimeter (mm) — 1/1000 of a meter. Used for precision measurements and technical drawings. Centimeter (cm) — 1/100 of a meter. Used for body measurements, clothing sizes, and everyday small measurements. Meter (m) — the SI base unit of length. Used for room dimensions, distances in sports. Kilometer (km) — 1,000 meters. Used for road distances and geographic distances. Imperial/US customary length units: Inch (in) — the smallest common imperial unit. Used for screen sizes, paper sizes, hardware, and US body measurements. Foot (ft) — 12 inches. Used for room heights, body height in the US, and altitude in aviation. Yard (yd) — 3 feet. Used in American football, fabric measurement, and golf. Mile (mi) — 5,280 feet. Used for road distances in the US and UK. Other length units you may encounter: Nautical mile — 1,852 meters, used in navigation and aviation. Light-year — approximately 9.461 x 10^15 meters, used for distances between stars.
Exact Conversion Factors and Formulas
These conversion factors are exact or rounded to sufficient precision for practical use. Centimeters to other units: 1 cm = 10 mm 1 cm = 0.3937 inches 1 cm = 0.03281 feet 1 cm = 0.01 meters Inches to other units: 1 inch = 2.54 cm (exact, by international agreement) 1 inch = 25.4 mm (exact) 1 inch = 0.08333 feet 1 inch = 0.02778 yards Feet to other units: 1 foot = 30.48 cm (exact) 1 foot = 0.3048 meters (exact) 1 foot = 12 inches Meters to other units: 1 meter = 100 cm 1 meter = 3.28084 feet 1 meter = 39.3701 inches Kilometers to other units: 1 km = 1,000 meters 1 km = 0.62137 miles Miles to other units: 1 mile = 5,280 feet 1 mile = 1,609.344 meters (exact) 1 mile = 1.60934 km Conversion formulas: Centimeters to inches: divide by 2.54 Inches to centimeters: multiply by 2.54 Feet to meters: multiply by 0.3048 Meters to feet: multiply by 3.28084 Kilometers to miles: multiply by 0.62137 Miles to kilometers: multiply by 1.60934
Practical Length Conversions for Everyday Life
Height conversion is one of the most common personal length conversions. The US uses feet and inches while most other countries use centimeters. Common heights in both systems: 5'0" = 152.4 cm 5'2" = 157.5 cm 5'4" = 162.6 cm 5'6" = 167.6 cm 5'8" = 172.7 cm 5'10" = 177.8 cm 6'0" = 182.9 cm 6'2" = 187.9 cm To convert feet and inches to centimeters: multiply total inches by 2.54. For example, 5 feet 9 inches = 69 inches x 2.54 = 175.26 cm. Screen and device sizes measured in inches (diagonal): 6 inches = 15.24 cm (smartphone) 13 inches = 33.02 cm (laptop) 27 inches = 68.58 cm (desktop monitor) 55 inches = 139.7 cm (TV) Running distances: 1 mile = 1.609 km 5K = 5 km = 3.107 miles 10K = 10 km = 6.214 miles Half marathon = 21.097 km = 13.109 miles Marathon = 42.195 km = 26.219 miles Cooking pan sizes: 8 inch pan = 20.3 cm 9 inch pan = 22.9 cm 13 x 9 inch pan = 33 x 23 cm
Length Conversion in Technical and Professional Contexts
Professional and technical contexts require precise length conversions with more decimal places than everyday use. Engineering and manufacturing: Technical drawings in the US use inches and fractions or decimal inches. International drawings use millimeters. The conversion is 1 inch = 25.4 mm exactly. Common engineering conversions: 1/16 inch = 1.5875 mm 1/8 inch = 3.175 mm 1/4 inch = 6.35 mm 1/2 inch = 12.7 mm 1 inch = 25.4 mm 2 inches = 50.8 mm Lumber sizes: US lumber uses nominal sizes that differ from actual dimensions. A 2x4 is actually 1.5 x 3.5 inches = 38.1 x 88.9 mm. Paper sizes: US letter size is 8.5 x 11 inches = 215.9 x 279.4 mm. International standard A4 is 210 x 297 mm = 8.27 x 11.69 inches. Aviation: Altitude is measured in feet in aviation worldwide, including in metric-system countries. This is a legacy convention maintained internationally for safety and consistency. Nautical navigation: Nautical miles are used for sea and air navigation. 1 nautical mile = 1,852 meters = 1.150779 statute miles.
Frequently Asked Questions
- How do I convert feet and inches to decimal feet?
- To convert feet and inches to decimal feet, divide the inches by 12 and add to the feet. For example, 5 feet 9 inches = 5 + (9/12) = 5 + 0.75 = 5.75 feet. To convert decimal feet to feet and inches, take the decimal portion, multiply by 12, and round to the nearest inch.
- Why is an inch exactly 2.54 centimeters?
- Before 1959, the US and UK used slightly different values for the inch relative to metric units. In 1959, the US, UK, Canada, Australia, New Zealand, and South Africa signed the International Yard and Pound Agreement, which defined 1 yard as exactly 0.9144 meters. This automatically makes 1 foot = 0.3048 m exactly and 1 inch = 0.0254 m = 2.54 cm exactly.
- How many centimeters in a foot?
- There are exactly 30.48 centimeters in one foot. This follows from the exact definition of 1 inch = 2.54 cm, since 1 foot = 12 inches and 12 x 2.54 = 30.48. To convert any number of feet to centimeters, multiply by 30.48. To convert centimeters to feet, divide by 30.48.