Honestly, I've never seem specifics on how much DE. ( Remember... food quality DE only.) In my coop I put a layer.. just like snow on top of the shavings and then put another inch of shavings on top. The chickens scratch around and mix it in. In my run (10X5) I sprinkle about a cup... again, it is like a lite dusting of snow. You can see it, but it's not a quarter inch thick. Then, I toss some shavings on top (about an inch thick). I chuck about a shovel full of lawn clippings on the shavings and the chickens mix it all together when they are scratching for the lawn clippings.
This guy at the feed store told me to put a kitty litter box with 2 inch play sand, 1 inch DE mixed together. The chickens all dust bathe in it and it keeps all the lice of 'em.
If it rains, the DE will no longer be useful so you have to do it again. Remember, use a mask and wear glasses when using this stuff. It's really fine dust and it stings the eyes and isn't good in the lungs! Apparently, no issue for chickens though... go figure