A method is proposed for calculating the amount of interstitial space, or habitat space in the L or O1layer of the hardwood forest floor. Assessment of habitat space may be useful for comparing litter environments in studies of litter-dwelling arthropods and other invertebrates. The method, an extension of the standard litter measures of depth and volume, includes litter structure as a quantitative factor. Data indicate that habitat space in the litter layer varies with structural composition and moisture accumulation.