there is no real ratio that always works, you have to factor your yeast into the situation.
1.02 = sweet mead. I like k1v1116, which hits around 16% (unless your using apple juice, then it hits 18ish....). So to make a sweet mead I make a must (mead wort) at like 1.145, which is about 2 gallons honey 4 gallons water. 1.125 is about 16% alcohol (my yeasts tolerance), so add .02 to make sure it will finish up sweet to arrive at 1.145ish.
Say I want to make a mead with Icvd47, which has a tolerance of around 14%, or 1.105, and I want it to finish sweet. 1.105 + .02 = 1.125 starting gravity. around 21# honey, 6 gallon total volume, fill the rest with water. (1.75 gal honey, 4.25 gal water).
I usually add all the honey to one gallon of water and mix it up really well then add water until it hits within about one gallon of the desired total volume, then check the gravity, add water, mix, check gravity, etc....
I use the gravity calculator over on gotmead.com, use the drop down menu that's labeled" recipes and mead making" or go here:
http://www.gotmead.com/index.php?option ... &Itemid=16