This study addresses the controversy of how “leaf” conductances, gst, are related to the total “canopy” conductance, gc, commonly used in the “big-leaf” approach (i.e. the Penman-Monteith equation). A simple multi-layer canopy model was coupled with a Lagrangian dispersion matrix that provides the profiles of temperature, humidity and CO2 within the canopy. In order to simulate stomatal behavior, we incorporated the empirical model presented by Ball, Woodrow and Berry; leaf conductance is thus dependent on net assimilation, relative humidity and CO2 concentration at the leaf surface. This study examines the effects of sw, friction velocity, leaf area magnitude and distribution, soil parameterization and atmospheric conditions on the relationship between gst and gc.