How do you figure out your enterprise value?

I am thinking of offering an IPO, but before I do, I want to know what the enterprise value of my company is as the IPO will offer 20% of it.

Thanks!

As much as I remember it's the equity value.

Here you go. This is what I have been reading for the last semester. Enjoying figuring out how to value an enterprise!

http://kanellopoulos.files.wordpress.com/2012/08/principles-of-corporate-finance-10th-edition.pdf

/Semi-kidding