Measuring the shore platform width might be an effective way to measure the rate of coastal retreat. The processes controlling shore platforms are a highly debated topic throughout the coastal science community. Some researchers believe that marine processes control them and other researchers believe that physical weathering is responsible. This study determined the relationship between rock mass classification systems and shore platform widths as a diagnostic tool to predict the rate of recession. Testing took place along the Mahia Peninsula and Tatapouri on the East Coast of New Zealand. A Garmin eTrex hand-held GPS unit was used to map both the cliff base position and the edge boundary of the shore platform. Data analysis for Mahia Peninsula showed a linear relationship with a r2 value of 68% with a negative regression line. The data for Tatapouri showed that there was no linear relationship, but has an r2 value of 68% when a polynomial fit to the 2nd order was apply to the data (appendix). The estimated rate of erosion, ranges from 0.61 to 17.8 0.06 mm y-1 for Mahia Peninsula and 1.32 to 16.45 0.08 mm y-1 for Tatapouri.