The modern world relies more and more on highly available software and digital data. To make this possible, the demands on data centers are increasing to provide the services in the required quality. This is associated with an increase in their power consumption and thus also their CO2 emissions. Today, they are already among the largest consumers of electricity and producers of CO2. Due to climate change and the set target of limiting global warming to a maximum of 2° Celsius, the aim is to reduce CO2 emissions. To calculate the CO2 footprint of data centers, data center simulators are already used in their planning phases. Simulators provide operators with important information about the future data center and show room for improvement. This thesis deals with the calculation of the Co2 footprint of data centers, the associated factors and provides an extended approach to the calculation of the CO2 footprint. Using a life cycle assessment approach, it is shown how the carbon footprint of data centers can be comprehensively calculated. For this purpose, several life cycle stages are determined that contribute to the CO2 footprint during the life cycle of a data center. Based on the life cycle stages, requirements for simulators are developed and, with the help of these, four current data center simulators are evaluated in their ability to calculate a CO2 footprint. Since current simulators calculate the CO2 footprint only partially and incompletely, the analysis of this work shows the need for a new simulator. Based on the analyzed life cycle stages, a new simulator is therefore designed. The subsequent evaluation of the simulator implemented as a proof-of-concept against the established requirements shows that the CO2 emissions of a data center can be comprehensively calculated with the demonstrated concept. In addition, a case study is carried out based on the High-Performance Computing Center Stuttgart and compared with the environmental statement of the HLRS.