Purpose: Although numerous publications have described distraction osteogenesis (DO) for craniosynostosis, methods of reporting quantitative results have been inconsistent. Therefore, the efficacy of anterior DO and posterior DO in regards to volume change is not well established. We report a metric that relates volume change to distraction length and our analysis of ICV change by distraction osteogenesis. Methods: Patients with craniosynostosis were treated with open cranial vault reconstruction combined with internal distraction. Preoperative and postoperative CT scans were used to quantify ICV change. Our metric was calculated by dividing percent ICV change by total distraction length. Multiple linear regression was used to identify the impact of distraction approach (anterior vs. posterior), age, time between CT scans, distraction length, and preoperative volume on ICV change. Additionally, we compared our findings to those reported in the literature. Results: Nine unicoronal craniosynostosis patients underwent anterior distraction. Three bicoronal patients and 1 multisutural patient underwent posterior distraction. The average ICV increase was 1.6% per millimeter of distraction for anterior DO compared to 4.2% for posterior DO (p<0.05). On multiple regression, preoperative volume was negatively associated with percent volume change (p<0.05). Posterior approach was positively associated with percent volume change (p<0.05). The volume-length relations from institutional data were greater than those derived from the literature, but not statistically significant. Conclusion: We report relations between distraction length and intracranial volume change for posterior and anterior DO and a comparison to the literature. Additionally, we describe a novel metric for analyzing ICV change achieved by DO.