A lumen measuring device generally includes a central member dimensioned to extend into a lumen and an elongate outer member having a flexible region configured to flex outward from the central member in response to retraction of the central member. In measuring a lumen, the flexible region is caused to contact the lumen. The lumen may be contacted by linear segments that hinge or by members that bow arcuately. A polygon, such as a triangle, may be defined by portions of the outer member and the central member. A handle assembly may be provided by which the disposition of the central member relative to the outer member may be adjusted. Indicators may be defined by the central member and outer member by which the disposition of the central member and by which the diameter of a lumen may be determined.