em Font-Size Scaling

I'm the parent with font-size: 2em;

I have a total width of 30em.

Div Left H2

I'm font-size: .5em; and my parent is font-size: 2em;

I am 50% of my parent's font-size now. I am back to the browsers default font-size.

I have a total width of 15em.

I'm font-size: 1.5em; and my parent is font-size: 2em;

I am 150% of my parent's font-size now.

I have a total width of 15em and it is in relation to my font-size.