Hartree (Eh) to Electronvolts Converter

About this calculator

The hartree (Eh) is the atomic unit of energy used in quantum chemistry and computational physics, defined so that it equals twice the ionization energy of a hydrogen atom in its ground state: 1 Hartree = 27.211386 electronvolts = 4.3597447 × 10⁻¹⁸ joules. Working in Hartree atomic units lets quantum-chemistry software drop most physical constants (reduced Planck constant, electron mass, elementary charge) from its equations by setting them to 1, which simplifies both the math and the numerical precision of the calculation.

Computational chemists and physicists running ab initio and density functional theory (DFT) packages (like Gaussian, ORCA, or VASP) constantly convert Hartree output — orbital energies, reaction barriers, bond dissociation energies — into electronvolts or kJ/mol, since those are the units used in experimental spectroscopy and everyday chemistry.