Decadal limestone erosion rates from a 30-year study of St Pauls Cathedral, London are compared with recession rates derived from applying Lipfert's and Tidblad's dose-response functions to the available rainfall and sulphur dioxide data from central London. Comparison of the measured erosion rates and the dose-response function derived recession rates shows consistently higher loss for the measured erosion rates, between 49 and 35 microns per year for measured rates as opposed to 15–12 microns per year for derived rates. Measured erosion rates were 3.33 times as high as derived recession rates towards the start of the 30 year measurement period, falling to almost 2.75 times by the 2000s. Analysis of the disparity suggests that, despite the magnitude of the differences between the two methods, they both record the same patterns of decline in erosion rates as sulphur dioxide levels decline. The disparity may result from using a common index of erosion, loss of height, to express the outcomes of two different measurement systems quantifying surface loss in different ways.