Determining width percentage with variable

I am trying to determine the width of a div in order to create a chart, to do this i have put a calculation to a variable. However when i try to put that variable into the css style width i am getting an issue with the variable and percentage. When i run this the width comes back as 0, eluding to an error?

What is the correct syntax to make this work? Here is what i have currently:

<div class="bar" style="width:%">scored</div>

via Chebli Mohamed