The lack of a suitable method of comparing the form assemblages of pebbles in naturally occurring populations was identified during studies of the shorelines of Loch Earn. In the absence of a precise intercomparison system between the verbal descriptors, a numerical method is introduced based on the Sneed & Folk (1958) grid. This permits mean, single and double pebble-form field scores to be calculated. Average form values for ‘compactness’, ‘platiness’ and ‘elongateness’ are computed from rotations of the grid, and simple numerical values are derived to describe mean pebble populations. The technique enables some quantification of pebble-form diversity. Each form of analysis is demonstrated using real data from lake shorelines.