To track progress, use a free tool such as EcoIndex, Website Carbon Calculator or the GreenIT Analysis extension on your home page and most visited pages. These tools estimate user devices poorly, although devices account for about half of the real impact, and their results differ by a factor of 4 to 10 from one tool to another: keep to the same tool and track the change over time. For a reliable absolute value you need an LCA of the digital service that includes the user device and the manufacture of equipment: its uncertainty is 20 to 30% and it costs €5,000 to €15,000 excl. VAT.
Read the source article: Website carbon footprint: how to calculate and reduce it