Carbon accounting has become a valuable tool for expressing the fossil energy demand of products, organizational entities, or entire countries. About a decade ago, cities also began accounting their carbon emissions. The first major city to do so was London in 2009, stating a carbon footprint of 4.84 tCO2eq/(year*capita) for 2008. Nowadays, multiple rankings compare the carbon emissions of cities. For example, the Urban Land Magazine lists São Paulo as the city with the world’s lowest carbon emissions (1.4 CO2eq/(year*capita)). Such listings typically present the depicted emission values as scientifically indisputable numbers. However, a closer look at the applied methodology frequently reveals a wide range of implicit, often undisclosed assumptions at the foundation of the calculations. This paper analyses the uncertainties of carbon accounting on the city scale, using the example of the Red Sea resort town of El Gouna. The estimated value of El Gouna’s carbon footprint for the year 2014 is 14.3 tCO2eq/(year*capita). Third Scope emissions constitute the majority of El Gouna’s carbon footprint. Varying their underlying assumptions only slightly can lead to alterations of the results of more than 50%, questioning the robustness of the findings. To increase the robustness and the comparability of carbon accounting across cities, this paper suggests emphasizing Scope 1 and Scope 2 emissions, while limiting the role of Scope 3 emissions.