1] The linear relation between the strength of the Agulhas Current at nominal latitude 34°S and the gradient in sea level height anomaly across the current is investigated in a 1/10° resolution regional numerical ocean model. Our results show that the strength of the current can be estimated with reasonable accuracy using altimeter data, once it has been calibrated using in‐situ transport measurements. Three years of transport measurements provide a calibration with worst‐case correlation R = 0.78. In that case the errors in proxy transport have a standard deviation of 9.8 Sv, compared to a 20.2 Sv standard deviation of the transport time series itself. From these results we conclude that the design of the Agulhas Current Timeseries (ACT) experiment, a three‐year deployment of moorings across the Agulhas Current and along a TOPEX/ Jason altimeter ground track, will likely produce a good quality multi‐decadal time series of Agulhas Current strength. Citation: van Sebille, E., L. M. Beal, and A. Biastoch (2010), Sea surface slope as a proxy for Agulhas Current strength, Geophys. Res. Lett., 37, L09610, doi:10.1029/2010GL042847.