Degree of Freedom (DOF) is a numerical representation of how bodies can move relative to one another in a system. It may vary independently. A free body in space has six DOFs. When you add a constraint, such as a revolute joint, between two bodies, the constraint will remove DOFs from the system. For example, a revolute joint removes three translational DOFs and two rotational DOFs between two bodies. The total number of DOFs in the system is equal to the difference between the number of allowed body motions and the number of active constraints in the model. The information is displayed in the Motion Solver message file (*.msg) as shown in the figure below.

Figure 5.6: Degree of freedom in the message file

The number of constraints for each Joint is as shown in the table below. For a Boundary Condition, the number of constraints is determined by user input.