Kilo (Prefix) — Definition, Formula & Examples

Kilo is a metric prefix that means 1,000. When you put "kilo" in front of a unit, it multiplies that unit by 1,000 — so 1 kilogram equals 1,000 grams and 1 kilometer equals 1,000 meters.

The prefix "kilo-" (symbol: k) denotes a factor of $10^3 = 1{,}000$ in the International System of Units (SI). Attaching it to any base unit produces a unit one thousand times as large as the original.

Key Formula

1 \text{ kilo-unit} = 1{,}000 \text{ base units}

Where:

$\text{kilo-unit}$ = The unit with the kilo prefix (e.g., kilogram, kilometer)
$\text{base unit}$ = The original unit without a prefix (e.g., gram, meter)

How It Works

To convert from a kilo-unit to the base unit, multiply by 1,000. For example, 3 kilograms becomes

3 \times 1{,}000 = 3{,}000

grams. To convert from the base unit to a kilo-unit, divide by 1,000. So 5,000 meters becomes

5{,}000 \div 1{,}000 = 5

kilometers. The abbreviation for kilo is a lowercase "k," written directly before the unit symbol: kg, km, kL.

Worked Example

Problem: A road is 7 kilometers long. How many meters is that?

Recall the meaning: Kilo means 1,000, so 1 kilometer = 1,000 meters.

Multiply: Multiply the number of kilometers by 1,000.

7 \times 1{,}000 = 7{,}000

Answer: The road is 7,000 meters long.

Why It Matters

Kilo is one of the most common metric prefixes you will encounter in science class, cooking, and everyday life. Road signs display distances in kilometers, food labels list mass in kilograms, and data storage is measured in kilobytes — all built on this single idea of "times 1,000."

Common Mistakes

Mistake: Dividing instead of multiplying when converting from kilo-units to base units.

Correction: Kilo means 1,000 of something, so going from kilometers to meters you multiply by 1,000 (making the number larger). You only divide by 1,000 when going the other direction — from base units to kilo-units.