A research project was conducted on the use of centrifuge technology to characterize the expansive properties of a highly plastic clay. The resulting testing procedure allowed the measurement of the one-dimensional swell of a soil sample in the centrifuge. This paper focuses on the analysis of testing results, specifically how to determine the relationship between swell and effective stress of a soil using centrifuge testing. Samples under centrifugation are subjected to wide range of effective stress across the sample height due to an increased unit weight. A method is initially proposed to define a representative effective stress of the centrifuge sample, which can be used to relate the swell of the sample to a single representative effective stress. A second, more robust method is also developed, which uses multiple centrifuge test results and curve fits a function to the data. Both methods were found to result in accurate swell-stress curves verified by comparison with curves determined by standard swell test methods.