A new description of ice VII, a cubic phase of water ice stable at pressures exceeding 2.1 GPa, has been developed. It describes the Gibbs energy, a fundamental thermodynamic potential energy from which many other thermodynamic quantities can be calculated, and covers pressures up to 500 GPa and temperatures up to 2,000 K using a flexible mathematical framework. Notably, it is the first representation of ice VII to incorporate data from both computational and experimental methods. It will allow for higher accuracy in studies of water-rich exoplanets, or planets outside the solar system that formed with many times the water content of Earth. These exoplanets are expected to possess abundant ice VII due to their high internal pressures, so the new representation will aid in the interpretation of telescope observations and assessments of their potential to host alien life.