A kilometer (km) is a metric unit of length equal to 1,000 meters, roughly six tenths of a mile. It measures long distances, such as the length of a road race or the distance between towns. To change kilometers to meters, multiply by 1,000: 3 km is 3,000 m.
One kilometer is 1,000 meters laid end to end, a little more than half of a mile. To change kilometers into a smaller unit, multiply; to go back, divide.
Formal definition and notation
The kilometer is a unit of length in the International System of Units (SI), equal to 1,000 meters; the prefix kilo- means one thousand. In the metric length table, 10 hectometers make 1 kilometer, so 1 km = 1,000 m = 100,000 cm. One mile is about 1.61 km, and one kilometer is about 0.62 mile.
Symbol
Read it as
Meaning
km
kilometer or kilometers
the unit symbol; it has no period and no s for plurals (5 km)
km/h
kilometers per hour
a speed: how many kilometers are covered in one hour
km2
square kilometers
an area unit for land, equal to a square 1 km on each side
Key facts
1 km = 1,000 m = 100,000 cm = 1,000,000 mm.
A kilometer is about 0.62 mile, so a mile is longer than a kilometer: 1 mile is about 1.61 km.
Road signs in most countries give distances and speed limits in kilometers and km/h.
A 5K race is 5 kilometers, about 3.1 miles; a 10K is 10 kilometers, about 6.2 miles.
The prefix kilo- means 1,000 for every metric unit: a kilogram is 1,000 grams and a kiloliter is 1,000 liters.
Kilometer conversions
Kilometer conversions
1 km = 1,000 m
km to m
multiply by 1,000 (move the decimal point 3 places right)
m to km
divide by 1,000 (move the decimal point 3 places left)
km to mi
multiply by about 0.62
mi to km
multiply by about 1.61
Going to a smaller unit gives a bigger number: 2.5 km = 2,500 m. Going to a bigger unit gives a smaller number: 750 m = 0.75 km.
Try it: convert kilometers
Interactive
Type a length, then pick the units to convert from and to. The staircase shows how many steps, and powers of 10, separate the units. Try 3.5 kilometers to meters, then swap the units.
This interactive needs JavaScript. The worked examples below show the same ideas step by step.
Kilometer examples, step by step
Example 1: Kilometers to meters
Warm-up
A hiking trail is 4.5 km long. How many meters is that?
Each kilometer is 1,000 meters, so multiply by 1,000.
4.5 × 1,000 = 4,500: the decimal point moves 3 places right.
Sense check: meters are much shorter than kilometers, so the number of meters should be much larger than 4.5.
Answer: The trail is 4,500 meters long.
Example 2: Meters to kilometers
Core
A bus route is 2,750 m long. Write the length in kilometers.
Going to a larger unit means a smaller number, so divide by 1,000.
2,750 ÷ 1,000 = 2.75: the decimal point moves 3 places left.
Sense check: 2,750 m is between 2,000 m (2 km) and 3,000 m (3 km).
Answer: The route is 2.75 km long.
Example 3: Laps and miles in a 5K
Test-style
A 5K race is 5 km. How many laps of a 400-meter track is that, and about how many miles, using 1 km ≈ 0.62 mile?
Convert to meters first, so both lengths use the same unit: 5 × 1,000 = 5,000 m.
Laps: 5,000 ÷ 400 = 12.5.
Miles: 5 × 0.62 = 3.1.
Trap: 5 ÷ 400 mixes kilometers with meters and gives 0.0125 laps.
Answer: A 5K is 12.5 laps of the track, about 3.1 miles.
Common mistakes
✗ MistakeA kilometer is shorter than a meter, because km is a different unit.
✓ Instead1 km = 1,000 m, so a kilometer is 1,000 times longer.
A kilometer is much longer than a meter, not shorter. The prefix kilo- means one thousand.
✗ Mistake3 km = 3 ÷ 1,000 = 0.003 m
✓ Instead3 km = 3 × 1,000 = 3,000 m
When you change to a smaller unit, you need more of them, so the number gets bigger. Multiply, do not divide.
✗ Mistake1 km = 100 m
✓ Instead1 km = 1,000 m (it is 1 m that equals 100 cm).
Centi- means one hundredth and kilo- means one thousand. Mixing up the prefixes is the usual source of this slip.
✗ MistakeA 10 km run is 10 miles.
✓ Instead10 km ≈ 10 × 0.62 = 6.2 miles.
A kilometer is shorter than a mile, so the number of miles is smaller than the number of kilometers.
A meter is the base metric unit of length, a little longer than a yard. A kilometer is 1,000 of them.
Kilometervs.Mile
A mile is a U.S. customary unit of about 1.61 km. A kilometer is metric and is about 0.62 mile, so a mile is the longer of the two.
Kilometervs.Kilogram
A kilogram is 1,000 grams, a unit of mass, not length. It shares the prefix kilo-, meaning 1,000, with the kilometer.
Quick check: 3 questions
Question 1 of 3
How many meters are in 7.2 km?
Show answer and explanation
Answer: B. Multiply by 1,000: 7.2 × 1,000 = 7,200 m. 720 multiplies by 100 (the centimeter factor), 72,000 by 10,000, and 0.0072 divides instead of multiplying.
Question 2 of 3
Which distance is the longest?
Show answer and explanation
Answer: C. Write them all in meters: 1,200 m, 900 m, 1,500 m and 1,050 m. So 1,500 m (1.5 km) is the longest. Comparing 1.2 with 1,500 directly mixes units.
Question 3 of 3
What is 3,400 m + 2.8 km, in kilometers?
Show answer and explanation
Answer: A. Change 3,400 m to 3.4 km, then add: 3.4 + 2.8 = 6.2 km. Choice B adds the numbers without converting, choice C converts 2.8 km the wrong way, and choice D gives the answer in meters but labels it km.
Kilometer: frequently asked questions
How many meters are in a kilometer?
There are exactly 1,000 meters in 1 kilometer. The prefix kilo- means one thousand, the same as in kilogram (1,000 grams). So 2 km is 2,000 m, 0.5 km is 500 m, and 0.025 km is 25 m. To convert, move the decimal point three places: right for kilometers to meters, left for meters to kilometers.
How long is a kilometer in miles?
A kilometer is about 0.62 mile, and a mile is about 1.61 kilometers. Multiply kilometers by 0.62 to estimate miles: 10 km is about 6.2 miles. Multiply miles by 1.61 to estimate kilometers: 26.2 miles is about 42.2 km. These factors are rounded, so answers are approximations.
Is it kilometer or kilometre?
Both spellings name the same unit. Kilometer is the U.S. spelling and kilometre is used in British English and many other countries. The symbol is the same everywhere: km, in lowercase, with no period and no s for the plural. Write 5 km, not 5 kms or 5 Km.
LengthLength is how long something is: the distance from one end of an object to the other. You measure it by counting equal units laid end to end with no gaps or overlaps, such as inches, feet, centimeters or meters. A new pencil is about 7 inches long.Measurement · Grade 1, Grade 2, Grade 3Equal ToEqual to means having exactly the same value or amount, and it is written with the symbol =. Numbers that look different can still be equal to each other: 12 is equal to 0.5. When two amounts are not the same, one is greater than or less than the other.Symbols and Notation · Kindergarten, Grade 1, Grade 2MeterA meter (m) is a metric unit of length equal to 100 centimeters. It is the base unit of length in the metric system, a little over three feet (about 3.28 feet). A doorway is about 2 meters tall, and 1,000 meters make a kilometer. To change meters to centimeters, multiply by 100.Measurement · Grade 3, Grade 4, Grade 5MileA mile (mi) is a US customary unit of length for long distances, equal to 5,280 feet or 1,760 yards. One mile is about 1.61 kilometers, so it is longer than a kilometer. Road distances and speed limits in the United States use miles and miles per hour.Measurement · Grade 4, Grade 5, Grade 6PeriodThe period of a repeating function is the horizontal length of one complete cycle: the smallest distance after which the graph repeats exactly. y = sinx and y = cosx have period 2π, or 360°, and y = tanx has period π. For y = sin(Bx) or y = cos(Bx), the period is 2π|B|.Trigonometry · Algebra 2, PrecalculusSquareA square is a quadrilateral with four equal sides and four right angles. It is a special rectangle and a special rhombus at the same time. For a square with side s, the perimeter is 4s, the area is s2, and each diagonal is s√2.Geometry · Kindergarten, Grade 2, Grade 3SideA side is one of the straight line segments that form the outline of a polygon. Two sides meet at each corner, or vertex. A triangle has 3 sides and a square has 4, and adding the lengths of all the sides gives the perimeter.Geometry · Kindergarten, Grade 1, Grade 2KilogramA kilogram is the base unit of mass in the metric system (SI), equal to 1,000 grams. Its symbol is kg. A liter of water has a mass of about 1 kilogram, and 1 kilogram is about 2.2 pounds. Kilograms measure heavier things, such as people, bags of flour or luggage.Measurement · Grade 3, Grade 4, Grade 5GramA gram is a metric unit of mass, about the mass of a paper clip. Its symbol is g. There are 1,000 grams in a kilogram and 1,000 milligrams in a gram. Grams measure light things, such as food portions, coins and letters; heavier things are measured in kilograms.Measurement · Grade 3, Grade 4, Grade 5Decimal PointA decimal point is the dot that separates the whole-number part of a number from its fractional part. Digits to its left are ones, tens and hundreds; digits to its right are tenths, hundredths and thousandths. In 46.25 the point sits between 6 ones and 2 tenths, and you read it aloud as “and”.Number System · Grade 4, Grade 5, Grade 6NumberA number is an amount or value used to count, measure, order and compare. We write numbers with digits (7), words (seven) or other symbols, but the number itself is the amount: 7 dots, the word seven and the numeral 7 all show the same number. Numbers include whole numbers, fractions, decimals and negatives.Number System · Kindergarten, Grade 1, Grade 2YardA yard (yd) is a US customary unit of length equal to 3 feet or 36 inches. It is a little shorter than a meter: 1 yard is exactly 0.9144 meter. Yards measure fabric, rooms, gardens and the length of a football field, which is 100 yards between the goal lines.Measurement · Grade 2, Grade 3, Grade 4DecimalA decimal is a number written with a decimal point to show parts of a whole. Decimals use place value to represent tenths, hundredths, thousandths and more: in 3.14, the 1 means 1 tenth and the 4 means 4 hundredths. So 0.75 = 75100, and 0.5 is one half.Number System · Grade 4, Grade 5, Grade 6Place ValuePlace value is the value of a digit based on its position in a number. In 3,507 the 5 is worth 500, because it sits in the hundreds place. Each place is worth 10 times the place to its right: ones, tens, hundreds, thousands, and after the decimal point, tenths and hundredths.Number System · Grade 3, Grade 4, Grade 5Unit ConversionUnit conversion is rewriting a measurement in a different unit without changing the amount, such as writing 3 feet as 36 inches. You multiply by a conversion factor, a fraction equal to 1 such as 12 in1 ft. Converting to a smaller unit gives a larger number; converting to a larger unit gives a smaller number.Measurement · Grade 4, Grade 5, Grade 6Unit RateA unit rate is a rate that compares a quantity to one unit of another quantity, such as 50 miles per hour or 4 dollars per notebook. To find it, divide the first quantity by the second: 150 miles in 3 hours is 150 ÷ 3 = 50 miles per hour. The word per means for each one.Ratios and Proportions · Grade 6, Grade 7, Grade 8CentimeterA centimeter is a metric unit of length equal to one hundredth of a meter, about the width of a fingernail. Its symbol is cm. There are 100 centimeters in 1 meter and 10 millimeters in 1 centimeter, and 1 inch equals 2.54 centimeters.Measurement · Grade 3, Grade 4, Grade 5Metric SystemThe metric system is a system of measurement in which units are related by powers of 10. Its base units are the meter for length, the gram for mass and the liter for capacity. Prefixes name larger and smaller units: kilo- means 1,000, centi- means one hundredth and milli- means one thousandth, so 1 km = 1,000 m.Measurement · Grade 4, Grade 5, Grade 6