A method and apparatus for measuring size distribution of bulk matter consisted of randomly orientated granules, such as wood chips, make use of scanning the exposed surface of the granular matter to generate three-dimensional profile image data defined with respect to a three-coordinate reference system, The image data is segmented to reveal regions associated with distinct granules, and values of the size-related parameter for the revealed regions are estimated. Then, a geometric correction to each ones of estimated size-related parameter values is applied, to compensate for the random orientation of corresponding distinct granules. Finally, the size distribution of bulk matter is statistically estimated from the corrected size-related parameter values.