This method is intended to measure the cladding diameter and noncircularity of optical fibers. This method is intended to be used on Class IV single-mode fibers. Although other fiber classes may be measured by this method@ details of the applicability have yet to be determined. In this method@ the motion of one or more components of a white light Michelson interferometer is measured precisely@ using a second (monochromatic) interferometer. This motion can be related to the fiber's cladding diameter. The main advantages of this method are a) high precision@ b) no reliance on surface contacts or edge definition@ and c) measurement of fiber diameter relative to a wavelength of light. Because of c)@ the insmment could@ at least in principle@ be internally calibrated. This method is intended for laboratory use@ with possible use for the creation of transfer standards. In the current implementation@ the equipment and procedures are not recommended for routine production or field measurements.