In short
- 1Divide centimeters by 100,000 to get kilometers.
- 21 km = 1,000 m = 100,000 cm.
- 3Moving the decimal point five places left gives the same result: 250,000 cm → 2.5 km.
- 4Map scales such as 1:100,000 rely on this: 1 cm on the map is 1 km on the ground.
Centimeters to kilometers table
| Centimeters (cm) | Kilometers (km) |
|---|---|
| 1 | 0.00001 |
| 2 | 0.00002 |
| 3 | 0.00003 |
| 4 | 0.00004 |
| 5 | 0.00005 |
| 6 | 0.00006 |
| 7 | 0.00007 |
| 8 | 0.00008 |
| 9 | 0.00009 |
| 10 | 0.0001 |
| Centimeters (cm) | Kilometers (km) |
|---|---|
| 12 | 0.00012 |
| 15 | 0.00015 |
| 20 | 0.0002 |
| 25 | 0.00025 |
| 30 | 0.0003 |
| 40 | 0.0004 |
| 50 | 0.0005 |
| 60 | 0.0006 |
| 75 | 0.00075 |
| 100 | 0.001 |
Reading map scales
The most common use of this conversion is a paper map. On a 1:50,000 map, 1 cm stands for 50,000 cm on the ground, which is 0.5 km. On a 1:25,000 hiking map the same centimeter is 250 m, and on a 1:250,000 road atlas it is 2.5 km.
To measure a route, lay a string along it, measure the string in centimeters, multiply by the scale number and divide by 100,000. A 12 cm trail on a 1:25,000 map is 12 × 25,000 ÷ 100,000 = 3 km.
Digital maps show a scale bar instead of a ratio, because zooming changes the scale. Printed maps keep the ratio, so the conversion above still applies to them.
Why metric steps are powers of ten
Every metric length unit is the meter with a prefix: centi means one hundredth and kilo means one thousand, as listed in NIST's SI prefix table. Going from centi to kilo crosses five powers of ten, so the conversion never needs a calculator, only care with the decimal point.
For the steps in between, cm to m and km to m cover one prefix at a time, and km to cm runs this page in reverse.
For very long or very short distances, scientific notation helps: 1 cm is 10⁻⁵ km, and 10⁵ cm is 1 km.
Cm to km questions
How many centimeters make up one kilometer?
100,000. A kilometer is 1,000 m and each meter is 100 cm.
What is 1,000,000 cm in km?
1,000,000 ÷ 100,000 = 10 km.
How far is 1 cm on a 1:100,000 map?
Exactly 1 km. The scale means 1 cm on paper stands for 100,000 cm on the ground.
Is it easier to convert through meters?
Often, yes. Divide by 100 to get meters, then by 1,000 to get kilometers. The two smaller steps are easier to check than one jump of five zeros.