An apparatus for adjusting the force in a door operator or closer includes a tube rotatable about a longitudinal axis and a coil spring therein connected to door operator/closer. A fixed adjusting screw extends along the longitudinal axis of the housing through the coil spring and a spring collar is threaded onto the adjusting screw and rotatable with the tube. The spring collar bears on the distal end of the spring to vary the spring compression upon rotation of the housing and thereby vary force applied by the door operator or closer. The housing has an opening though which the spring is visible, and the tube has markings indicating the degree of spring compression. An indicator is moveable along and visible outside the housing to indicate the compression of the spring.