A task chair equipped with a mechanism for independently adjusting the height and width of support arms by the manual operation of a single adjustment knob. Each of the support arms includes a first arm portion and a second arm portion that are pivotally coupled by corresponding pivot joints. Each second arm portion carries one of a pair of arm pads. Each second arm portion may be inclined relative to the corresponding first arm portion for inclining the corresponding arm pad relative to a seat plate of the task chair. Each arm pad is joined with the corresponding second arm portion by a coupling mechanism that permits movement of each arm pad with two degrees of translational freedom and one degree of rotational freedom.