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Convert between metric and imperial lengths with exact factors.
Convert lengths between millimeters, centimeters, meters, kilometers, inches, feet, yards, and miles. Uses exact international definitions — 1 inch is exactly 2.54 cm — so results are precise enough for engineering homework and DIY alike.
Length is the most converted quantity in daily life, and its units come in two great families. The metric family — millimeters, centimeters, meters, kilometers — scales by tens and is the standard almost everywhere. The imperial and U.S. customary family — inches, feet, yards, miles — dominates in the United States and lingers in Britain for road distances and human height. The bridge between them is exact: since the 1959 International Yard and Pound Agreement, one inch equals exactly 2.54 centimeters, which fixes the foot at exactly 30.48 cm, the yard at exactly 0.9144 m, and the international mile at exactly 1,609.344 m. The nautical mile, used in aviation and shipping worldwide, is exactly 1,852 meters.
Different trades favor different units, which is why conversion never goes away. Construction and interior design in the U.S. think in feet and inches; runners think in kilometers or miles depending on the country; aviation measures altitude in feet but distances in nautical miles everywhere on earth; fabric is sold by the yard in America and the meter elsewhere. Scientific work uses meters and its decimal relatives exclusively. Knowing which unit your audience expects is half the battle — converting correctly is the other half, and this calculator handles the arithmetic.
Convert by multiplying with the exact factor, keep full precision until the final step, and round the answer to match your measurement's precision. Going from metric to imperial, divide by the same factor (or multiply by its reciprocal): meters to feet uses 3.28084, kilometers to miles uses 0.621371. For rough mental math, remember 1 m is about 3 ft 3 in, 1 km is about 0.6 miles, and 1 inch is about 2.5 cm — good enough for estimating, but use the exact factors for anything you will build, buy, or dose.
Every unit converts through meters with its exact factor: 1 inch = 0.0254 m, 1 foot = 0.3048 m, 1 yard = 0.9144 m, 1 mile = 1609.344 m. The result is value × factor[from] ÷ factor[to].
The exact factor is 30.48 cm per foot. Multiply: 6 x 30.48 = 182.88 cm, or 1.8288 m. Going the other way, a person who is 183 cm tall is 183 / 30.48 = 6.0039 feet — essentially 6 ft 0 in (0.0039 x 12 = 0.05 inches of rounding). This is the conversion behind every height question on forms, IDs, and medical records, and because the factor is exact, there is no approximation debate: 6 feet is 182.88 cm, period.
The exact factor is 1.609344 km per mile. Multiply: 26.2 x 1.609344 = 42.1648, rounded to 42.16 km. The official marathon distance is 42.195 km, which corresponds to 26 miles 385 yards — the 26.2 figure is a rounded shorthand, and the 0.03 km gap is the rounding, not an error. Reverse check: 42.195 / 1.609344 = 26.219 miles. Runners comparing a 10K personal best across countries use the same factor: a 40-minute 10K is 40 / 6.21371 = 6.437 minutes per mile, or 6:26/mile pace.
Enter 5, choose km → mi: about 3.107 miles. The exact factor is 1 km = 0.621371 mi.
Multiply by 2.54 — or just use this tool. 12 inches is exactly 30.48 cm.
Yes. An international inch is defined as exactly 2.54 cm, and a mile as exactly 1609.344 m, so every conversion here is exact to full precision.