The gravimetric and volumetric energy densities of lithium ion batteries are key parameters for their implementation in real-life devices, yet to date, these values are documented differently both in academic and industrial reports, which makes the comparison of advances in this field challenging. This ambiguity stems from calculation methods that take into account different battery components and since certain cell design parameters such as the mass loading and electrode density are often omitted, it is difficult to find out what assumptions are made in the calculations. Herein, we present calculation methods for the specific energy (volumetric) and energy density (gravimetric) that are appropriate for different stages of battery development: (i) material exploration, (ii) electrode design, and (iii) cell level engineering. These calculations help establishing a fair and robust method to compare energy metrics, and we highlighting the calculation details that must be specified in reports to understand the reported figures unambiguously. Finally, we calculate how some key battery design parameters such as the mass loading, electrode density and N/P ratio affect the energy metrics