A fiber optic probe has been used to measure spout diameters in a half-column and a full-column based on the significantly higher counts of output electric pulses in the spout region than in the annulus. The flat wall of a semi-cylindrical spouted bed column was found to cause considerable distortion of spout shapes which became approximately semi-elliptical in cross-section. Caution must therefore be exercised when using spout diameter data from the face of half-columns for spouted bed modelling and design. The often-used McNab (1972) equation was found to underestimate the spout diameters in the full-column, with an average deviation of 35.5%.