AbstractA 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%.