Slider bearing gaps are often measured using the white light interference spectrum from the narrow gap between the slider and a spinning glass disk. Using that same interference data, one can also estimate the amplitude of the first oscillatory mode of the slider. This paper illustrates this method with simulations and with actual interference data. This approach uses conventional white light interferometry data and requires no additional hardware or modification of equipment. It can be extended to estimate amplitudes of higher frequency modes.Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in Toronto, Ontario, Canada, October 8–10, 1990