It varies a lot according to the system you use.
So far the most efficient and klutz proof for me is the Caldera Cone , I use the Ti version with a 550ml pot. I just boil water and re-hydrate inside a Decor container (solo use....) or freeze dry meals as i did recently.
My typical use is a mug of coffee in the morning (350-450 ml) about the same for the evening meal plus another 300ml or so for cocoa, and a cup of coffee (or soup when cold) every second lunch or so.
On a recent trip , 10 days total, I used just under 500ml .
A typical figure mentioned is 1 oz to boil 500ml .
Some systems will need about twice as much if windy. This is where an enclosed version like the Caldera Cone (or the Trangia) comes out on top.
If you have not purchased your alcohol kit yet, have a look here :
http://antigravitygear.com/categories.php?cat=50or for the Titanium ( can burn wood as well with this one and the cone is a lot stronger and more flexible) :
http://www.titaniumgoat.com/TiTri.htmlFranco