Don't think of a hand drawing as being more complicated than anything else you draw...because really, it isn't.
When learning how to draw the human hand, you must familiarize yourself with the basic hand structure and proportions of the fingers, the thumb, the palm of the hand and the back of the hand. Add some practice and you are well on your way to drawing realistic hands.
This is a drawing I did of my hand for instructive purposes.
Note where the hand begins, (that area where the lower arm turns into the wrist). This is indicated by line 1 on the drawing.
Line 2 indicates the first set of knuckles. These knuckles are the base of the fingers. This is the point at which the "body" of the hand stops and the fingers begin. The "body" coincides with the palm on the other side of the hand.
The bulk, or the body of the hand starts at line 1 and ends at line 2, as seen in this diagram.
Line 3 indicates the end of the fingers. Note that the body of the hand (line 1 to line 2) is approximately equal in length to the length of the fingers (line 2 to line 3).
Even if not exact, finding these approximations is very helpful in learning how to draw hands (or any other parts of the human figure.)
As in all drawing, first you have to find the general proportions...and then you can "zero" in from there, in order to get accurate detail.
The second set of knuckles (line 4) is approximately halfway between the first knuckles (line 2) and the end of the fingers (line 3).
Note that the thumb begins approximately in the middle of the body of the hand (A).
If the thumb was in closed position, the top of the thumb would end at the first knuckle. (See line B)
All of the above guidelines are general approximations which allow you to simplify your approach to drawing hands. Look carefully at your own hands and see for yourself.
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