Measurement of diesel smoke in an accurate and consistent manner has been a serious problem for engine and vehicle manufacturers, users, and agencies charged with enforcing smoke limits. Several instruments, based on different principles and using different scales, are commonly used. In addition to these, human observation and judgement are often used to relate smoke to a variety of standards. The purpose of this SAE Information Report is to provide an understanding of the nature of diesel smoke, how it can be measured, and how the various measurement methods can be correlated. Except for defining the various types of smoke, the report deals solely with the steady-state measurement of visible, black smoke emitted from diesel engines.