Usually the rating for torque is something like oz-in which is a simple multiplication of the mass times the distance from the hub.
If we ignore the mass of the arm, a 60 oz-in servo can move 60 ounces at 1 inch from the center of the hub. The same torque would be required for 30 ounces at 2 inches, 10 ounces at 6 inches, 2 ounces at 30 inches... Unfortunately you cannot ignore the mass of the mounting, which makes the equation a little more complex. If you have a dowel rod ( uniform mass distribution), you can figure the entire mass to be concentrated at the halfway point. If you have something complex, like a skeleton arm, you need to consider the mass of each piece at its average distance from the center of the hub.
RM