When one says "ideal" size survival knife, I think of a 12" camp machete. But like self-defense guns, practical usually trumps ideal. It is hot down here, so most folks wear little clothing in summer. My Kimber 1911 is an "ideal" self defense pistol, but I am not going to walk around the mall with it on my belt. My little .380 fits in my pocket, so it gets carried. The same is true of "survival" knives. The one I carry is the SAK OHT, along with my Rat Trap.