Dense metallic grids can create surfaces that are conductive at microwave frequencies yet optically transparent. However, fullwave solutions of such grids are computationally expensive. To accelerate simulations of complex structures we consider three approximate models for a wire grid. Circuit-based models provide estimates of radiation efficiency for simple antennas without simulating the complex gridded structure. However their accuracy is limited, typically yielding efficiency 13% from the actual value. As an alternative, an effective surface impedance can be assigned to the grid. In this case, the error in efficiency averages only 3.4%, but a fullwave simulation is required, albeit less costly than simulation of the grid itself.