Over a decade after the introduction of sentencing guidelines in England and Wales, little is known about their effects on consistency and individualisation. Limited research has addressed the issue of consistency, and no research has explored another key concept, namely individualisation. This is regrettable since one criticism of guidelines is that they undermine the principle of individualisation at sentence, and this critique is examined here. The article explores two potential threats to individualisation, using sentence length data from the Crown Court Sentencing Survey. One threat may arise if a guideline constrains judges to sentence within a restricted range, leading to a less individualised approach to sentencing. The second is more fundamental, and consists of the tendency to favour some sentence lengths over others – a preference for certain ‘round’ numbers. The article reports an analysis of custodial sentences for assault offences. Results indicate that sentence lengths for assault offences are affected by a preference for certain numbers – a tendency first observed by Francis Galton in the 19th century. On a more positive note, we find no evidence that the sentencing guidelines for assault and burglary introduced in 2011 have diminished the degree of individualisation in sentencing. We also find that courts report taking a larger number of sentencing factors into account under the new guidelines, further evidence that the guidelines have not undermined individualisation.