Blow-out fractures affect the volume and surface area of the orbital cavity. Estimation of these values after the trauma may help in deciding whether or not a patient is a candidate for surgery. Recent studies have provided estimates of orbital volume and area of bone defect, and correlated them with the degree of enophthalmos. However, a large degree of biological variation between individuals may preclude such absolute values from being successful indicators for surgery.Stereological methods have been used to estimate orbital cavity volume in a few studies, but to date these have not been used for surface area. To authors' knowledge, this study is the first to have measured the entire surface area of the orbital cavity.The volume and surface area of the orbital cavity were estimated in computed tomography scans of 11 human cadavers using unbiased stereological sampling techniques. The mean (± SD) total volume and total surface area of the orbital cavities was 24.27 ± 3.88 cm and 32.47 ± 2.96 cm, respectively. There was no significant difference in volume (P = 0.315) or surface area (P = 0.566) between the 2 orbital cavities.The stereological technique proved to be a robust and unbiased method that may be used as a gold standard for comparison with automated computer software. Future imaging studies in blow-out fracture patients may be based on individual and relative calculation involving both herniated volume and fractured surface area in relation to the total volume and surface area of the uninjured orbital cavity.