  The PADME experiment at the LNF Beam Test Facility searches for dark photons
produced in the annihilation of positrons with the electrons of a fix target.
The strategy is to look for the reaction $e^{+}+e^{-}\rightarrow \gamma+A'$,
where $A'$ is the dark photon, which cannot be observed directly or via its
decay products. The electromagnetic calorimeter plays a key role in the
experiment by measuring the energy and position of the final-state $\gamma$.
The missing four-momentum carried away by the $A'$ can be evaluated from this
information and the particle mass inferred. This paper presents the design,
construction, and calibration of the PADME's electromagnetic calorimeter. The
results achieved in terms of equalisation, detection efficiency and energy
resolution during the first phase of the experiment demonstrate the
effectiveness of the various tools used to improve the calorimeter performance
with respect to earlier prototypes.
