Roll structure measurement is presently done with destructive and intrusive measuring devices, such as Force Sensing Resistors (FSR) [1] or with specially instrumented winders. These methods are generally limited to research and development applications. Prior to this project, there was no method of non-destructively determining the internal stresses, or roll structure, with unknown winding conditions. This thesis presents a measurement technique, the Acoustic Roll Structure Gage, that uses acoustic time of flight (T.O.F.) measurements to determine roll structure, an extension of the work done by J. David Pfeiffer [2] and alluded to by L. Eriksson [3] and D. R. Roisum [4]. A measurement is made of the time required for an acoustic wave to travel through the roll. This time of flight measurement is used as an extra degree of freedom in a winding model such as Z. Hakiel's [5] to replace an unknown or questionable model input, such as radial modulus or winding tension. The roll structure is determined by iterating the model input until the calculated time of flight matches the measured time of flight. This measurement technique is called the Acoustic Gage. The Acoustic Gage was verified by comparison with two other independent methods, FSR' s [1] and pull tabs [4]. Each method was used to map the radial pressures in the left and right sides of six different wound rolls. The Acoustic Gage agreed with two other independent roll structure measurement tools, all of which were much lower radial pressure than predicted by winding models. The results cast doubt on the validity of the hoop stress equation as an outer boundary condition for wound roll models. This thesis discusses pertinent literature, roll structure fundamentals, preliminary experiments and, acoustic and wave propagation topics. The equipment and procedures for time of flight measurements in wound rolls, including the method of determining roll structure from time of flight measurements are presented.