There are a number of units that can be used to describe **mass**, from pounds, ounces and tonnes to stones and grams.

We are going to focus on the most common of these which is the metric measurement **g*** rams*.

All of the units you will have heard of are based around the root word 'gram' with other words tacked on to describe their relationships:

**Kilo**gram - 'Kilo' means 1000 so **1 kg = 1,000 g**

**Centi**gram - 'Centi' means 100 so **1 cg = 100 g ***(This one is rarely used.)*

**Milli**gram - 'Milli' means 1000 so **1 g = 1,000 mg**

**How to Convert Between Different Units **

**Step 1:** Decide on our conversion factor (i.e. g to kg needs to use a conversion factor of 1,000)

**Step 2: **Either multiply or divide by this number to reach our converted value.

Let's look at this process in action now with some examples.

**e.g. Convert 150 g into kg.**

**Step 1:** Decide on our conversion factor.

1,000 g = 1 kg so our conversion factor is **1,000**.

**Step 2:** Multiply or divide by this conversion factor.

We need to think about this a little to decide whether to multiply or divide.

One way to look at this is that a kilogram is bigger than a gram, so there needs to be fewer of them overall.

As there needs to be fewer of them, we need to divide:

**150 ÷ 1,000 = 0.15 kg**

**e.g. Convert 280 g into milligrams.**

**Step 1:** Decide on our conversion factor.

1,000 mg = 1 g so our conversion factor is **1,000**.

**Step 2: **Multiply or divide by this conversion factor.

A milligram is smaller than a gram, so there will need to be more of them overall.

As there needs to be more of them, we need to multiply:

**280 × 1,000 = 280,000 mg**

In this activity, we will practise converting between the four units of mass measurement described above (kilogram, centigram, milligram and gram) using the method we have seen in action here.