We describe the design, fabrication, and calibration testing of a new piezoresistive cantilever force sensor suitable for the force calibration of atomic force microscopes in a range between tens of nanonewtons to hundreds of micronewtons. The sensor is calibrated using the NIST Electrostatic Force Balance (EFB) and functions either as a force reference or stiffness artifact that is traceable to the International System of Units. The cantilever has evenly spaced fiducial marks along its length. We report stiffnesses that vary quadratically with location, from a high of 12.1 N/m at the first fiducial to a low of 0.394 N/m at the last; with force sensitivities that vary linearly, ranging from 18.1 Ù/mN to 106 Ù/mN. We also test the device to transfer the unit of force to an atomic force microscope, finding that force and stiffness based approaches yield independent estimates of the contact force consistent within 2 % of each other.