The equation of state (EOS) for hot, dense matter in massive stars relates energy and pressure to temperature, density, and composition. The EOS influences the shock formation and evolution in core collapse supernova, and determines the compactness of the nascent proto-neutron star. We constructed an EOS of nuclear matter for a wide range of temperatures, densities, and proton fractions for use in supernova and neutron star merger simulations. We employed a fully microscopic relativistic mean field calculation for matter at intermediate density and high density, and the Virial expansion of a nonideal gas (with nucleons and 8981 kinds of nuclei) for matter at low density. This work computed the EOS at over 180,000 grid points in 3-dimensional parameter space (temperature, density, and proton fraction). The most time consuming part involved relativistic mean field calculations for nonuniform matter. There were over 15,000 grid points in mean field calculations, where most points took several hours to one day to calculate. We applied Message Passing Interface to calculate different points in parallel. The overall calculations took over 7,000 CPU days in Indiana University supercomputer clusters. We used bicubic Hermite interpolation with slope limiter to generate a thermodynamically consistent big table. Our new table is ready for use in astrophysical simulations of core collapse supernova and neutron star mergers. It is an improvement over existing EOS tables. It should provide important new input for the study of supernova explosions and for predicting gravitational wave signals from mergers simulations.