Torque is defined as twisting force. To calculate the torque around the rotation of a crank caused by a weight at the end of the crank, you need to multiply the weight times the horizontal distance from the center of gravity of the weight to point of rotation.

**Unit of Torque:**

The International System of Units, SI, (the French Système International (d’unités)), suggests using the unit newton meter (N⋅m). The unit newton meter is properly denoted N⋅m or N m. This avoids ambiguity with mN (millinewtons).

In Imperial units, “pound-force-feet” (lbf-ft), “foot-pounds-force”, “inch-pounds-force” are used. Other non-SI units of torque include “meter-kilograms-force” are also used. For all these units, the word “force” is often left out. For example, abbreviating “pound-force-foot” to simply “pound-foot” (in this case, it would be implicit that the “pound” is pound-force and not pound-mass).

**Maximum and Minimum Counterbalance Moment:**

The crank generates maximum torque when it is in a horizontal position. This maximum torque is known as the “**Maximum Counterbalance Moment**” ( **maximum** **CBM**) expressed in inch-pounds.

**NB:** In rod pumping, the CBM is expressed in thousands of inch pounds.