Studies of the response of the SiD silicon-tungsten electromagnetic calorimeter (ECal) are presented. Layers of highly granular (13 mm^2 pixels) silicon detectors embedded in thin gaps (~ 1 mm) between tungsten alloy plates give the SiD ECal the ability to separate electromagnetic showers in a crowded environment. A nine-layer prototype has been built and tested in a 12.1 GeV electron beam at the SLAC National Accelerator Laboratory. This data was simulated with a Geant4 model. Particular attention was given to the separation of nearby incident electrons, which demonstrated a high (98.5%) separation efficiency for two electrons at least 1 cm from each other. The beam test study will be compared to a full SiD detector simulation with a realistic geometry, where the ECal calibration constants must first be established. This work is continuing, as the geometry requires that the calibration constants depend upon energy, angle, and absorber depth. The derivation of these constants is being developed from first principles.
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