The study of spiritual development has been challenged by difficulties with definitions and measurement. Different faith traditions place different values on various aspects of spiritual development, yielding different definitions with implications for the measurement of the construct. This study focuses on measurement of postconventional religious reasoning, which is a specific, measurable aspect of spiritual development with clear parallels in cognitive development. This research focuses on the Revised Faith Development Scale (RFDS), a 16-item Likert instrument that is easier to administer than previous interview measures of postconventional religious reasoning and more reliable than a previously developed self-report measure. Preliminary assessment of convergent validity indicators support the use of the RFDS.