This is a revised and much-compressed version of two threads that I posted in another place. Some of the conclusions I draw sound like they might have some kind of actual math behind them, and they do. But I have chosen not to include it here, because time and attention are the most valuable commodities on the Internet. If you're reading, I will try not to waste yours. Some knives work better for EDC than others. Beyond the obvious difficulty of opening a letter with your 8" Bowie knife, there isn't a whole lot of information out there about exactly why some knives just seem to "feel better" than others. All people say is "great ergonomics!", if they say anything at all. I'm here to kill that magic for you. With one simple line. For those who care about photo quality, you won't find it, here: I copied them into Paint, and drew a line on them. So they're different sizes, and all kinds of things that would send a proper photographer into convulsions. So what? That's not the point. The point is that little black line across the knife. This line is part of the "feels good" quality of any knife. It starts at the point, and just barely touches the part of the handle where your index finger should naturally rest. From there, it passes out of the back of the handle. Let's look at another. This is a wharncliffe-blade version of the Hinderer Flashpoint, which is the fixed-blade version of the XM folder. For those who like their accuracy. RH's knives are one of the things that people generally agree have "great ergonomics!", which is what got me thinking about this question. Back to this mystery line. If you look at the pommel of the knife, you'll see that it crosses the end of the handle up higher (toward the spine), than it did on the drop point. One more example. This triumph of form over function is brought to you by Benchmade. The line is red this time, like it should have been in the other pictures, but Paint is a stupid program to work with. Never mind. Much of everyday cutting involves getting the point of the knife into the thing you want to cut. Many common materials have great shear- and tensile strength, making it hard to open bags and taped boxes. So the measure of a knife that functions well is how natural it feels to control the tip. For some reason, that "natural" feeling is determined by where that red(/black) line ends. There is more to it than that, but very little meaningful work is being done to compare folding knives. A lot of noise goes into lock strength, and steel chemistry, but the bestest, strongest, sharpest knife is going to stay in a drawer, because it has to have a lot more qualities than just superior cutting ability. The line that I've drawn in those pictures is only part of the story. The rest of this post is another part. As mentioned above, I have decided to omit large portions of the original thread. It began with a couple knives from my collection that I enjoyed carrying, because I felt they were good examples of what a knife handle should feel like in use. It continued with measurements of width and thickness at a key point on the handle, and a comparison of perimeter and aspect ratio, to reach the conclusions you see, below. For a knife to "feel good", it must have Perimeter of 2.56 inches (distance around), at the point where you index finger naturally grips the handle. This one is up for debate, because I can't speak for people at either end of the bell curve, hand-size-wise. It may be that a “better” formula is a comparison ratio of your hand length to the perimeter of the knife handle. Aspect Ratio of 0.46 to 0.75, inclusive, to allow for good control while cutting. This width-to-thickness ratio is also measured at the point where you index finger grips the knife during regular cutting tasks. Finally, that “tip to pommel line”. I haven't come up with a slick name for it, but it's a graphical representation of how easily you will be able to control the tip of any knife. The further up the spine of the handle that line touches, the better. There is more to it, still. I've concentrated on the index finger, but the rest of your hand plays a role, too. I've got some ideas, but I haven't found a way to put them into words, just yet. I'm posting all of this because I want to encourage discussion. My conclusions sound really good (to me), and I'm the first person to address this with math. But I'm especially interested in why you think I'm wrong, what else you would like to see me try to figure out about knives, and what you would do differently.