Stem biomass estimates are useful for various purposes. For example, the amount of commercially usable timber, carbon stock and energy fuel potential are directly related to biomass quantity. This paper describes the development of a biomass flexible equation for poplar (Populus x canadensis I - 488) combining stem profile and basic wood density models, which were fitted and validated with a sample of 60 trees of this variety of poplar. The biomass equation, which is obtained from the double integral of the product between the basic wood density and cross-sectional stem area, was analyzed in four scenarios given by combining average and individual tree models for both stem profile and basic wood density. The most accurate results in both stem profile and basic wood density modeling, as in the stem biomass estimates, were obtained with individual tree models.