# Unit Conversion

Many people have problems converting units from one type to another, commonly there are questions such as:

*"If I change from millimetres to metres do I multiply or divide by 1000?"*

With this method, you will no longer have to worry about this confusion. There are a couple of simple steps which I will describe with an example, we want to convert

*metres per second*into

*kilometres per hour*

**1: Write down what you want to convert**

V = 15m/s

**2: Write down necessary conversions**

1000m = 1km

3600 seconds = 1 hour

**3: Multiply by 1**

this is easiest shown by example but basically we have:

1000m = 1km

Therefore [math]1 = \frac{1km}{1000m}[/math]

and 3600 seconds = 1 hour [math]1 = \frac{1hr}{3600s}[/math]

we can substitute these 1's into our 15m/s which becomes:

[math]V = 15\frac{\frac{m\color{red}km}{\color{red}1000m}}{\frac{s\color{blue}hr}{\color{blue}3600s}}[/math]

because we have multiplied by 1, the result is unchanged only now we have a more complicated way to write it with more units and fractions which will soon be removed.

**4: Cancel and multiply out**

[math]V = 15\frac{3600km}{1000hr}[/math] which becomes

[math]V = 54\frac{km}{hr}[/math]

This method is simple and effective. It's only problem is that it takes more time but it is worth it if you often make simple mistakes in unit conversions.