Abstract: A ring sizer which can be inserted into an inside circumference of a band portion of a ring in order to self adjust the ring size to a wearer's finger, the ring sizer including a plurality of elongated body sections having their end portions nestingly arranged with respect to each other. Each of the body sections is constructed to straddle the band portion of the ring. An arcuately shaped leaf spring functions as a retaining bar for supporting all of the body sections in a longitudinally adjacent relationship, with the body sections thereby forming an arcuate configuration. An arcuately shaped leaf spring functions as a biasing bar, which is curved in an opposing direction to the retaining bar to engage the ring band portion so that the arcuate configuration of the body sections conforms to the wearer's finger.