You know. . .thats a real good question. . . I honestly don't know.
I know in 1999, I measured them at 17.25 inches. Now, I really don't take measurements. . I let the scale and the mirror do the talking.
To tell you the truth, I don't consider my arms a strong point. . my torso muscles (back, chest, and delts) have always out done my arms. I have relatively long limbs, so pressing movements have always been a challenge. I have to have really big upper arms to shift around the nasty stuff.
You might as well call me Mike Katz.
As far as the avatar, it might be the angle of the shot. . .this shot was taken from my webcam.
I hope this helps.