Knife Handle Ergonomics 101: Getting A Grip On The Basics

Design factors are crucial in matching the knife handle and the hand.

It all started with a stone. Held between the thumb and index finger, it could be used to cut things efficiently if the user learned how to keep the edge sharp.
It was the birth of knife technology.

The next step was to attach the stone to a stick. The stick handle afforded more versatility on how the stone blade could be used. Even though it started out looking like a mere piece of broomstick, there is some obvious utility in it since many knives today have the same simple shape. As a result, though knife handle technology did advance quickly at first, it really hasn’t changed that much in several thousand years. The reason is hand ergonomics. There are only so many ways a handle can fit into the human hand, though small differences in handle design can sometimes be profoundly important.

I bet that, as a knife collector, you have handled hundreds of knives and often exclaimed, “This knife is perfect.” We all have. What did we mean? What were we thinking? I would also bet the knife handle fit very snugly in your hand when you thought that. You were able to get a firm grip while you envisioned yourself using the knife on a camping trip, or perhaps defending your life, or doing a multitude of different tasks. The handle wasn’t too big, nor too little. There were no pressure points or sharp contours that caused discomfort. Your approval of the handle was probably appropriate to the task you were contemplating. However, while all blade configurations are not well suited for every possible task, likewise, for best use the knife handle design must complement the blade to which it is attached.

Cutting Jobs

Let’s simplify knife tasks into four basic categories:

1. First are the simple everyday cutting chores, better known as “everyday carry” stuff. Open a package, cut a string, peel an apple, it’s just EDC. You think any tool with a sharp edge will do—and you’re right;
2. Second is where you must open 500 cardboard boxes or a similar job that takes some degree of force and puts a lot of stress on your hand;
3. Third is where you slice 10,000 tomatoes. Well, private, that’s a rough eight-hour shift in the mess hall! Many kitchen knives have some very non-ergonomic handles. Not a big deal if you’re cutting just one tomato, but in eight hours of doing that your hand might actually get some permanent damage. Yes, permanent;
4. Fourth is an oft-used example and the pinnacle of all scenarios: defending your life. Oh yes, there has been many a knife made for extreme situations. It’s fun to own a big bowie!

The perfect handle for an EDC has so much latitude that the word perfect doesn’t seem like it should ever be used. Going to the other extreme of the fourth category, the concern would be on grip strength. You would not want to lose hold of the knife during a life-or-death situation. A handle that provides a good grip probably would sacrifice some versatility, though in an extreme situation grip strength is probably more important than versatility.

Size

Is the size of the handle’s diameter really important? There is some leeway here, but once you get into endless tomato and box cutting and especially the need for maximum “grip strength” during life-and-death situations, it is a very important factor. According to many studies, as the handle diameter is progressively increased, so too is the grip strength—at least up to a certain point. After that, grip strength starts to decrease.

It is a bit odd that shoe sizes come in a variety of lengths, even half sizes, and also various widths, but gloves are basically small, medium, large and extra large. Why not size gloves more like shoes? The expression “fits like a glove” might mean you are lucky to find a pair that actually fits.

Does one size fit all? Yes, sometimes. But just like buying shoes, you have to put them on and walk around the store a while. If you plan to climb a mountain, you better be damn sure that the shoes will fit, perform and not cause blisters. If a knife handle feels good, then is it good? Probably so. There are many knife handles that “look good” but the proof is how they feel in your hand, your particular hand.

Knife Handle Diameter

Gripping round sticks/knife handles of different diameters results in different ergonomic effects.

The first example shows less than optimal grip strength with a thin handle having diminished contact area between the palm and the handle surface. The force is maximum when the thumb and fingertips are directed parallel to the palm.

The second example favors a strong grip. The fingers are also able to wrap around the handle and there is more surface contact available.

The third example is near the peak of biomechanical advantage. Grip strength might be a little improved from the second example or perhaps a little diminished. Not very different there. Importantly, the thumb and fingers can still cross over each other. There is more advantage from friction. This might be the best fit for a baseball bat. Yet for a knife there will be less ability to change the hand position, which may be a disadvantage. Some consider a diameter of about 1.5 inches to offer the strongest grip and this example is a little larger than that.

The fourth example is loss of grip strength. The fingers can’t encase the handle. The strong ergonomic “power grip” is transforming to the ergonomically weaker “pinch grip.” —by LeRoi Price

Hand vs Handle

We already know about handle diameter. What about shape? Though the round shape of a broom handle works for a knife handle, an oval configuration fits well into the hand and, importantly, allows for indexing of the blade’s cutting edge. Most knife handles have a basically oval cross section.

Form follows function but it begins with ergonomics. There are several dedicated handle configurations that are suited well to a special purpose but are mainly limited to use for that single special purpose. One of the most notable examples is the karambit handle. Asymmetric handles can improve the grip but also limit versatility.

The anatomy, ergonomics and biomechanics of the hand present some challenges for handle design.

Palm Anatomy

Prominent features of palm anatomy play a pivotal role in hand ergonomics. The red line is the actual bending point of the fingers. The blue dots are where the fingers bend from the palm. The green dashes are the second of the three bending points of the fingers. The yellow squares represent the prominence of the base of the thumb. The black hyphens indicate the small prominence of the heal of the hand. The oval of white squares is a hollow space in the center of the palm.

Note: the hand is not like a door hinge. These lines move as the hand goes from flat open to a closed fist. Now look at the back of your hand as it goes from open to a fist. The knuckles go from a fairly flat line to a downward curve. The finger joints all have a different radius at which they bend.
Hand ergonomics is not a static condition, which makes things difficult for handle design.

Handle Subtlies

Here is a simple camp knife and somebody made it right. I’ll point out my reasons why starting with the finger groove (B). It is well demarcated though not deep nor very pronounced—just like all the subtle features of this handle. This allows the handle to be more easily manipulated than if the fingers are forced into deep recesses. The groove fits the index finger.

A slight forward rise (A) forms an integral guard. This is an important feature. Some knives like this one have a brass guard in front that is not just mere decoration. A rising protrusion (C) fits into the space of the middle and index fingers. Then it’s down to the groove where the little finger resides (D). Another protrusion (E) captures the little finger and forms a rear guard—again, important for a camp knife.

Area “F” extends more rearward and slopes down to contact the heal of the hand. A slight swell (G) fits into the palm. Some knives are flat in this area but that doesn’t fit hand anatomy well. The handle has a very subtle hollow at “H.” This is where the web of the thumb makes contact, which makes it best to keep it subtle. Area “I” rises slightly here but often is left flat in many knives. This is where you place your thumb when doing some tasks. Putting a guard on the handle spine is less effective than putting one underneath because there are no bones in the thumb web—though slightly rising at “I” is useful.

Conclusion

There is no agreement on the shape of the perfect handle, so you are left with my opinion. On the other hand, you have something to think about and can investigate further. My opinion is this: While there is no such thing as “perfect,” there is still “good enough.” The same can be said for a lot of things.

I shouldn’t give numbers but I know you’re going to be curious about some. For a 5-foot-8-inch man, shoe size 9D which correlates to a large size glove, the handle configuration should be oval with a top-to-bottom dimension of 1.125 inch and 1 inch width. These suggestions are approximate, of course, but are the actual dimensions of the pictured camp knife seen with a handle length of 4.675 inches. (Go up to perhaps 1.5 inches height for a combat knife.) The back of the handle should be convex as well as the lower belly. A shallow groove for the index finger is a good option, and perhaps a second one for the middle finger as well. More finger grooves improve grip strength but are a detriment to the ability to manipulate the knife. They also add pressure points.

When you find a knife handle that doesn’t feel right, it is probably not right for you. Nonetheless, finding one that fits your hand “good enough” is probably the best you can do, and all you need to do.

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