Smoldering spread rates (cm h-1) are derived from the results of an experimental evaluation of the unit area burning rate of smoldering material (g cm-2 h-1). The unit area burning rate, which is the load loss rate normal to the smoldering surface, depends only on the moisture and inorganic content of the smoldering material. A derivation shows how the smoldering spread rate can be expressed as the ratio of the load loss rate to the organic bulk density (g cm-3). A nomogram estimates the smoldering spread rate in terms of the organic bulk density, and the moisture and inorganic contents of the fuel bed. © by the Society of American Foresters. Abstract reproduced by permission.