Uh...what?
The nut is the bit of bone/plastic/graphite at the end of your fingerboard, by the headstock. The width there varies between 42 and 45mm, give or take (up to 1.75" wide). The width of the rest of the fingerboard is defined by the spacing of the strings at the bridge. Draw it out full size, mark the width of the nut, move the outer strings in about 3mm from the edge, draw the lines for the outer two string paths (from nut to bridge, proper spacing), and then add lines 3mm outside that where the fingerboard ends. Sounds all complicated, but it's dead simple. Overall, width of the fingerboard at 12th fret is usually about the same as the string spacing at the bridge. Width where the neck meets the body is entirely irellevant, and dependant on where the neck joins up.
Draw everything up in full. Buy Melvyn Hiscock's 'Make Your Own Electric Guitar' which will answer all of these questions in some detail. Seriously.
If you're talking about depth (how fat is the neck, front to back), the difference is smaller, and taste-related. between 19mm and 21mm at the nut (first fret), maybe a bit thicker, say 22-24mm at the bit before the heel.
Perfect, it definately makes sense now. I can't say I don't feel like an idiot though. Thanks for all the help.