A well-fitting and comfortable ischial containment socket relies on accurately replicating the transverse plane angle of the ischium and ischial ramus angle, inside the medial socket brim. Prediction of the ischial ramus angle, may provide a way to determine the ischial ramus angle without in vivo measurement.To determine the accuracy with which the ischial ramus angle could be predicted and identify which variables contributed significantly to the prediction.Cross-sectional study.Computed tomography scans were randomly sampled from a cadaveric database (n = 200). Standard multiple regression models were developed to predict the ischial ramus angle based on pelvic measures.The regression model explained 10.5% of the variance in ischial ramus angle (p = 0.018). The standard error of the estimate was 11.32°. While regression models by sex explained a larger proportion of the variance, the resulting accuracy was not improved.The regression models explained a small proportion of variance in ischial ramus angle. The average error associated with the prediction was too large to accurately predict the ischial ramus angle for use in clinical practice. Contrary to commonly held beliefs, there was no statistically significant difference in ischial ramus angle between sexes. Clinical relevance Prediction of ischial ramus angle does not have sufficient accuracy to be clinically useful, but descriptive data may help clinicians identify casting errors and correct these in a plaster positive, knowing that the average ischial ramus angle was 32.65°±5.59° (relative to mid-sagittal plane) and does not vary between sexes.