Optimal length for chef's knife?
What length do you most prefer? What length is most common/useful?
I have a 10", a 9", and several 8" chef knives. I prefer the 8 " knives for most uses. I still occasionally use the 10" knife but also find myself using a Chinese cleave for say, winter squash.
I bet 8" is most common. But I most enjoy my 10" Messermeister. I remember Sara Moulton, a very small woman, likewise wielding such a knife most of the time in her shows.
Despite the larger size, the tip is really good for small work (like routing out an eye in a potato), it's unbeatable for mincing garlic, and the greater length is handy for larger tasks (like slicing a flank steak, halving a melon, etc. I can't really remember a time when I felt the knife was too large for anything, except paring operations, like peeling an apple.
But as everyone will say, you need a knife that feels good in your hand. This is not one of those things to do over mail order, if you can avoid it.
Personal preference mainly. Though anything super short (like 5 inches) starts getting pretty limited in terms of things it can't cut easily.
I personally prefer Japanese chef knives, and with those I like both 240 and 270 mm blades (about 9.5 inches and 10.6 inches respectively). Most of these Japanese knives are so light and nimble that a 9.5 inch gyuto is as easy to control as an 8 inch Western chef knife.
Longer knives are more versatile (can cut bigger things & more things at the same time; they also make better slicers and work better for bread) but need more space and are harder to control. That 240 to 270 mm range feels right to me.
My favorite is a 10" carbon steel Sabatier, my trusty companion for several decades now. But my wife, who has very small hands, finds it too big for comfort and prefers her little six-incher.