I'm looking at that difference, for me, right now (two adjacent desks). It's about 15 1/4 inches (39 cm).

P.S. When sitting, I have my desk 1 - 1 1/2 inches lower than "typical", primarily to provide a better typing position.

I'm 6'1 and my eye-level difference is 13-inches. My monitor has 5 inches of adjustment.

If you think you need more than 12 inches you're slouching while you're sitting.

You're damn right I am!

But when I stand, I stand up straight. Or at least I slouch less.

It's not just about monitor placement though. Keyboard height, at least for me, is more important for a comfortable computing environment that monitor height.

Just checking now, I've got about 18-inches difference between my seated keyboard height and my standing keyboard height.

Interesting. I actually appreciate the low standing keyboard height in my setup. My setup is far from ideal, but does have some advantages.

META: why is my 5 ranked post at the top? There's more interesting posts more highly ranked further down. Because it has more comments? To those who care, I think `javan`'s post is the most relevant for somebody looking to make a cheap & easy desk.