Pile scour may cause instability to the structures they support. Ensuring a safe and economically sound design is essential for the wider community. Although much laboratory research has been carried out on scour at pile groups, there are still significant gaps in prediction formulae. This study has been conducted to develop a formula for scour at pile arrangements of non-uniform spacing. The study was based on a laboratory experiment found in the literature. Previous empirical formulae for uniformly spaced pile groups were first used to gauge an idea of their performance. The formula that predicted the scour depth more accurately was then modified. The approach of Ghaemi et al. (2013) outperformed the other trialled empirical formulas. Using this formula, a correction factor was suggested to increase the prediction accuracy. The gap to diameter ratio was also corrected to include the non-uniformity of spacing in two directions.