Glass manufacturing is an energy-intensive process where raw materials are melted at temperatures often >1400 °C. Sustainable glass manufacturing is becoming increasingly important as both the energy crisis of the 2020th decade and the climate crisis are spiring. CO2 emissions during the glass melting arise from three different sources, i) fuel combustion, ii) raw material decomposition and iii) power consumed by the production facility. Taking container glass as an example, which is the most produced glass product in the world, the recent trend has been to increase the recycling rates. Depending on the location of the container glass producer (i.e., the access to cullet), the color, and the quality demand, recycling of cullet is in the range of 30-90%. Increasing the recycling is a typical route to reduce the energy need for glass manufacturing, however, lightweighting is another viable option towards sustainability which so far has only been explored to a limited extent. To make a glass container lighter, the glass needs to be made stronger through a strengthening process which also requires energy. The theoretical estimation of the required energy for melting, annealing and strengthening a glass container is to be presented.