Length Conversion Guide: Meters, Feet, Miles, and More

12 min read•June 1, 2026•Reviewed: June 1, 2026

✓Reviewed by Apex Conversion Editorial Team · Last reviewed June 1, 2026

Length is the most fundamental measurement in everyday life. Whether you are following a construction blueprint, checking a body-height field on a form, estimating road distances when traveling abroad, or converting a furniture measurement between countries, you are constantly moving between metric and imperial length units.

This guide covers every length unit you are likely to encounter — meters, centimeters, millimeters, kilometers, inches, feet, yards, miles, and nautical miles — with the exact conversion formulas, practical reference anchors, common mistakes, and answers to the ten questions people ask most often.

What the Units Mean

Length units fall into two dominant systems. The International System of Units (SI) — the modern metric system — is used in almost every country on Earth for science, engineering, and everyday measurement. The US customary system is used primarily in the United States, though even American science uses SI. The UK uses a hybrid system in daily life, with metric for most purposes but miles on road signs.

Metric units are decimal: each unit is a power of ten multiple of the meter. Millimeter (mm) = 0.001 m. Centimeter (cm) = 0.01 m. Meter (m) = the SI base unit. Kilometer (km) = 1,000 m. Imperial and US customary units use non-decimal ratios: 12 inches per foot, 3 feet per yard, 1,760 yards (5,280 feet) per mile.

Nautical miles are a specialized unit used in aviation and maritime navigation. One nautical mile equals one arc-minute of Earth's latitude — approximately 1,852 meters or 1.151 statute miles. This geometric definition makes nautical miles ideal for chart navigation.

Common Units and Typical Uses

Millimeters (mm): precision manufacturing tolerances, rainfall amounts, bolt and screw diameters, medical imaging. Centimeters (cm): clothing measurements, body dimensions, screen sizes in many countries, tire widths. Meters (m): room and building dimensions, athletics track distances, athletic throws, weather balloon altitudes.

Kilometers (km): road distances, national park areas, geography, marathon race distances (42.195 km). Inches (in): US screen sizes, plumbing pipe diameters, US body measurements, furniture. Feet (ft): US room heights, building elevations, altitude in aviation, body height in the US. Yards (yd): American football, fabric and textile measurement. Miles (mi): US road signs, speed limits, marathon training. Nautical miles (nmi): aviation route distances, maritime navigation, weather reporting.

Key Conversion Formulas

━━━ METRIC ↔ IMPERIAL ━━━
  1 inch   = 2.54 cm   (exact)     1 cm   = 0.393701 in
  1 foot   = 0.3048 m  (exact)     1 m    = 3.28084 ft
  1 yard   = 0.9144 m  (exact)     1 m    = 1.09361 yd
  1 mile   = 1.609344 km (exact)   1 km   = 0.621371 mi

━━━ WITHIN METRIC ━━━
  1 m = 100 cm = 1,000 mm = 0.001 km
  1 km = 1,000 m = 100,000 cm

━━━ WITHIN US CUSTOMARY ━━━
  1 ft = 12 in     1 yd = 3 ft = 36 in
  1 mi = 1,760 yd = 5,280 ft = 63,360 in

━━━ NAUTICAL ━━━
  1 nmi = 1,852 m = 1.852 km = 1.15078 mi

Real-World Examples

Body height: A person who is 5 feet 9 inches tall is (5 × 12) + 9 = 69 inches × 2.54 = 175.26 cm = 1.75 m. Converting feet-and-inches to cm: multiply total inches by 2.54. Converting cm to feet-and-inches: divide cm by 30.48 to get decimal feet, then separate the integer and decimal portions.

Road distances: A 100-mile road trip is 100 × 1.609344 = 160.9 km. A 5K race is 5 km × 0.621371 = 3.107 miles. A marathon (42.195 km) is 26.22 miles. Quick mental estimate: multiply miles by 1.6 for km, or multiply km by 0.6 for miles.

Home renovation: A 12-foot ceiling is 12 × 0.3048 = 3.66 m. A 1,200 sq ft apartment is 111.5 m². A 6-inch water pipe has an inner diameter of 6 × 2.54 = 15.24 cm = 152.4 mm. Construction material dimensions almost always use inches or millimeters depending on country.

Common Mistakes to Avoid

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Confusing meters and yards: a yard is 0.9144 m — about 9% shorter than a meter. A 100-yard US football field is only 91.44 meters, not 100 meters.
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Forgetting that miles and kilometers are not similar in magnitude: 1 mile = 1.609 km. A 100 km/h speed limit is only about 62 mph, not 100 mph.
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Using 2.5 cm per inch (it is exactly 2.54): this 1.6% error compounds — over 72 inches (6 feet), it produces a 2.9 cm error.
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Squaring the wrong factor when converting area: 1 m² = 10.764 ft² (not 3.281 ft²). Divide by 10.764 or multiply by 0.0929 to convert ft² to m².
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Mixing feet-and-inches: always convert entirely to inches before multiplying by 2.54. 5 ft 7 in = 67 in (not 5.7 × 12).
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Using 'miles' when you mean 'nautical miles': at sea and in aviation, always specify nmi. 1 nautical mile ≠ 1 statute mile (1 nmi = 1.15078 mi).

Frequently Asked Questions

How many centimeters is 1 inch?

Exactly 2.54 centimeters. This is an international definition established in 1959. Since it is exact, all inch-to-cm conversions are exact — no rounding occurs at the definition level.

How many feet is 1 meter?

1 meter = 3.28084 feet. The inverse: 1 foot = 0.3048 m exactly. Since 1 foot is defined as exactly 0.3048 meters, this is an exact conversion.

How many kilometers is 1 mile?

1 mile = 1.609344 kilometers exactly. This follows from: 1 mile = 5,280 feet × 0.3048 m/foot = 1,609.344 m = 1.609344 km. A quick mental approximation: 1 mile ≈ 1.6 km (within 0.04%).

How do I convert cm to feet and inches?

Step 1: Divide cm by 2.54 to get total inches. Step 2: Divide by 12 to get feet; the integer part is feet, multiply the decimal by 12 for remaining inches. Example: 175 cm ÷ 2.54 = 68.90 in ÷ 12 = 5 ft + 0.74 × 12 = 5 ft 8.9 in.

How many meters in a mile?

1 mile = 1,609.344 meters exactly. This is useful for track athletics: a 1,500-meter race is slightly less than 1 mile (1,500 ÷ 1,609.344 = 0.932 mi). The mile run (1,609.344 m) and 1,500 m differ by 109.3 m.

What is the difference between a yard and a meter?

1 yard = 0.9144 meters (exact). A meter is about 9.36% longer than a yard. A 100-yard dash = 91.44 meters. The 100-meter Olympic sprint is equivalent to about 109.36 yards.

How many feet is 1 kilometer?

1 km × (1,000 m/km) × (3.28084 ft/m) = 3,280.84 feet. A kilometer is about 3,281 feet or just over half a mile (0.621 miles).

What is a nautical mile?

A nautical mile is 1,852 meters (1.852 km = 1.15078 statute miles). It equals one arc-minute of latitude on Earth's surface. Pilots and sailors use nautical miles because navigation charts measure distances in arc-minutes of latitude, making the conversion trivial.

How do I convert millimeters to inches?

in = mm ÷ 25.4 (since 1 in = 25.4 mm exactly). Example: a 6 mm bolt = 6 ÷ 25.4 = 0.236 in ≈ 15/64 inch. For the reverse: mm = in × 25.4.

How many miles is a marathon?

A marathon is 26.2188 miles (26 miles, 385 yards), defined as exactly 42.195 km. The distance is fixed worldwide. A half marathon is 21.0975 km = 13.1094 miles, commonly listed as 13.1 miles.

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