Effective radial setting expansion of wax patterns in a gypsum-bonded investment is influenced by many factors, especially by the diameter of the cylindrical casting ring. The hypothesis tested was that the ratio of the volume of the casting rings to the volume of the ring liner is a primary determinant of radial setting expansion. Mesio-occlusodistal inlay wax patterns were invested individually in plastic casting rings of different lengths and diameters and imaged using xeroradiography. Effective setting expansion was determined in 34-mm-long, 28-mm-diameter rings and used as a predictor of expansion in rings of different sizes. Experimental setting expansion results did not differ significantly from the predicted values.