Thread tensioner for a sewing machine. In one example embodiment, a thread tensioner for a sewing machine includes a first disk, a second disk, a spring, a knob, and a sensor. The second disk is positioned next to the first disk. The spring is configured to apply tension to a thread positioned between the first disk and the second disk by exerting a force against the second disk. The spring defines a length between a first end and a second end. The knob is configured, when rotated in one direction, to travel along a threaded shaft toward the spring and thereby cause the length of the spring to shorten. The knob is configured, when rotated in another direction, to travel along the threaded shaft away from the spring and thereby allow the length of the spring to lengthen. The sensor is configured to track a current length of the spring.