Flames are stretched due to the interactions between nonuniform flow along the flame, flamefront curvature, and flame motion. Variations in the stretch rate induce local variations in the flame temperature and the mass burning rate. Williams defined flame stretch as the fractional rate of change of an area element on a flame surface [1]. This definition assumes an infinitesimally thin reaction zone, a single chemical reaction and single Lewis number. On the other hand, De Goey et al. [2] and De Goey and Boonkkamp [3] derived expressions for the flame stretch for flames of finite thickness based on mass conservation. Their formulation is consistent with simulations of multidimensional reacting flows with multicomponent transport and finite rate chemistry [2,4]. Markstein [5] used a semi-phenomenological model to propose a linear relation between flame speed and flame stretch. Although the relation between flame stretch and flame speed is well described by the asymptotic analyses for weak stretch, a corresponding relation for flames with high values of strain rate and curvature is not well established. Flame tips provide a convenient topology for investigating the response of flames to strong hydrodynamic straining and curvature. Recently, Choi and Puri [6,7] experimentally investigated stretch effects on rich premixed methane-air slot-burner flames. They identified a planar region and a curved tip in these flames that responded differently. We compared the flame stretch predicted by the conventional thin flame and the mass-based thick flame definitions along curved flame tips through a numerical simulation of a methane-air flame established on a slot burner. Our focus on the flame tip was motivated by the premise that the effect of flame thickness could be expected to be most severe in regions of high flame curvature. The simulation was conducted with the NIST Fire Dynamics Simulator (FDS) developed by McGrattan et al. [8]. This code employs an approximate form of the Navier-Stokes equations that is appropriate for low Mach number flows in which chemical reaction is modeled through a single global step.