### What are Units?

**Units** lets us know exactly what a number is **refering to**.

If I were to tell you that ‘I ran 100’. You wouldn’t realy know what I meant. ‘Ran 100 what…?’ You might ask. That’s where units come in, they tell us what a number refers to.

If I said ‘I ran 100 meters’… it would make a lot more sense!

A lot of **units** to do with length, mass and weight start with either:

**milli**, **centi** or **killo**

Milli means **a thousandth**. For example a millimeter is 1 thousandth of a meter… in other words there are 1000 millimeters in 1 meter.

Centi means **a hundredth**. For example a centimeter is 1 hundreth of a meter… there are 100 centimeters in a meter.

Killo means **one thousand**. A killometer is 1000 meters.

### Units of Length

Units that measure length are quite straight forward.

A kilometer is **1000 meters**.

A meter is made up of **1000 millimeters**.

A meter is also made up of **100 centimeters**.

A centimeter is made up of **10 millimeters**.

### Units of Mass

An object’s mass is how heavy it is.

A kilogram is **1000 grams**.

Mass is sometimes measured in:

Stone, pounds and ounces

A stone is made up of **14 pounds**.

A pound is made up of **18 ounces**.

### Units of Volume

An object’s volume is the space that it takes up.

We talk about the **volume of 3D shapes** in another lesson, these are measured in:

cmÂ³

Liquids however are usually measured in:

Litres and millilitres

The volume of a liquid is sometimes called **capacity**.

A litre is made up of **1000 millilitres**.

A Liquid’s volume can also be measured in **pints**.