Abstract. Apracticalmeans of quanmingthe diffusivities of forest fuels from fielddata is presented. The mathematics of this method is explored for four fuel shapes: a litter layer, a hardwood leaf, a twig and a square fuel moisture analogue stick, which are represented geometrically by a semi-infinite solid, a slab, a cylinder and a square prism, respectively. Theresults are presented graphically. Analyses of two published sets of field data indicate defusivities of 4.1 x 10-12m2 s-1 and 1.3 x 10-10m2 s-1 for Eucalyptus leaves and twigs, respectively, and 2.9 x 10-9m2 s-1 for a lodgepole pine litter layer.