# Does the human hand have 27 degrees of freedom?

I have counted the degrees of freedom in my hand over and over and I keep getting the number 19.

Suppose each finger has 3 degrees of freedom. Then 5 * 3 = 15. The wrist can rotate around or back and forth so that contributes to 4 degrees of freedom. In total the hand has 19 degrees of freedom.

From a cursory google search, I can notice that it is commonly agreed upon that human hand has 27 degrees of freedom. Can someone provide a good reference and explanation for this?

• The first link in that search is a paper which says this: "The human hand has 27 degrees of freedom: 4 in each finger, 3 for extension and flexion and one for abduction and adduction; the thumb is more complicated and has 5 DOF, leaving 6 DOF for the rotation and translation of the wrist." Commented Mar 28, 2015 at 21:02
• @canadianer is there a video or some sort that I can visually see how this is the case? Commented Mar 29, 2015 at 5:11
• Why is this flagged as "unclear"? Hasn't @canadianer already provided the answer in the comment? Can't you answer it canadianer? Better to answer a question than have it deleted. Admittedly, it's quite a poor question but I am happy to edit it a bit after an answer is put forward
– AliceD
Commented Mar 30, 2015 at 23:00
• @AliceD I didn't answer because I don't know anything about it and the OP seems to want a better explanation. I don't think the question should be closed. Commented Mar 30, 2015 at 23:03
• @canadianer - yes I see his video comment. Personally, I think you should answer, you have my upvote :) But I understand your position. It won't result in an accepted answer I guess. Up to you!
– AliceD
Commented Mar 30, 2015 at 23:04

Keeping in mind that I know nothing about this, I will try to explain why the hand can be modelled with 27 degrees of freedom. This is just my interpretation of this paper, which says:

The human hand has 27 degrees of freedom: 4 in each finger, 3 for extension and flexion and one for abduction and adduction; the thumb is more complicated and has 5 DOF, leaving 6 DOF for the rotation and translation of the wrist.

To accurately model the hand, a complete model of the muscles, tendons, bones and a neurological control structure is necessary. The dynamics of such a complex model are still poorly understood, forcing the use of simplified models. Current models are too simplified for our purpose so we turn to recent work from the medical community to motivate assumptions used in a new model that we propose here. We use a 27 DOF model of the hand with the following sim- plifying assumptions: 1. The thumb is independent of the other fingers. 2. Adduction/abductionofthefingerjointsareindependent. 3. Motion frequency does not affect joint interdependence. 4. Both hands have the same interdependence model. 5. The posture of the wrist and the rest of the arm do not affect the underlying interdependence structure.

Incidentally, this implies to me that there are different models of the hand with different assumptions that use a different number of degrees of freedom.

Anyways, take a look at this hand:

[source]