This paper describes an experimental method for determining the maximum areal density achievable for a given head-to-tape interface (HTI). Using this method, we can calculate amplitude and bit-shift error rates during dropouts for the areal density the HTI is originally designed for, and beyond. First, the read-back waveform is sampled to obtain the amplitude distribution of signal samples below 50% clip level at each areal density. Second, the channel-transfer-function variation is investigated during a dropout to study its effect on the bitshift error rate. Third, empirical relationships between the areal density and an rms-to-rms signal-to-noise ratio (SNR) are obtained. Based on the above information, a theoretical model is presented that predicts the error rate for each areal density after a write skip (defined here as the soft-error rate). The calculated soft-error rate agrees well with its experimental counterpart. The technique presented here is useful in determining the upper limit of the HTI used in the paper.