Kilometre (Kilometer) — Definition, Formula & Examples

A kilometre (spelled kilometer in American English) is a unit of length in the metric system equal to 1,000 metres. It is commonly used to measure long distances, such as the distance between two cities.

The kilometre (symbol: km) is a unit of length in the International System of Units (SI) defined as exactly $1{,}000$ metres, or equivalently $10^3$ metres. One kilometre is approximately $0.621$ miles.

Key Formula

d \text{ (km)} = \frac{d \text{ (m)}}{1{,}000}

Where:

$d \text{ (km)}$ = The distance in kilometres
$d \text{ (m)}$ = The distance in metres

How It Works

You use kilometres to measure distances that are too large for metres to be practical. To convert metres to kilometres, divide by

1{,}000

. To convert kilometres to metres, multiply by

1{,}000

. For example, if a running track is

400

metres and you run around it

5

times, you have run

2{,}000

metres, which equals

2

km.

Worked Example

Problem: A family drives 8,500 metres from their house to the shops. How far is that in kilometres?

Step 1: Divide the distance in metres by 1,000.

\frac{8{,}500}{1{,}000} = 8.5

Answer: The shops are

8.5

km from the house.

Why It Matters

Kilometres appear on road signs, maps, and GPS devices in most countries around the world. Understanding this unit is essential for reading distances in geography, science, and everyday travel.

Common Mistakes

Mistake: Multiplying by 1,000 instead of dividing when converting metres to kilometres.

Correction: Remember that a kilometre is a larger unit than a metre, so the number of kilometres should be smaller. Divide metres by 1,000 to get kilometres.