  The energy reconstruction of extensive air showers measured with the LOFAR
Radboud Air Shower Array (LORA) is presented in detail. LORA is a particle
detector array located in the center of the LOFAR radio telescope in the
Netherlands. The aim of this work is to provide an accurate and independent
energy measurement for the air showers measured through their radio signal with
the LOFAR antennas. The energy reconstruction is performed using a
parameterized relation between the measured shower size and the cosmic-ray
energy obtained from air shower simulations. In order to illustrate the
capabilities of LORA, the all-particle cosmic-ray energy spectrum has been
reconstructed, assuming that cosmic rays are composed only of protons or iron
nuclei in the energy range between $\sim2\times10^{16}$ and $2\times10^{18}$
eV. The results are compatible with literature values and a changing mass
composition in the transition region from a galactic to an extragalactic origin
of cosmic rays.
