Not all carbon calculators are created equal…in fact, if you provide the same starting information to 10 different calculators, you will likely get ten totally different answers that could vary by several orders of magnitude. Does that mean that each of them is wrong? Not necessarily… part of the issue with calculating carbon emissions today comes from what assumptions are made and what standards are used in the calculations. There is no single “right” carbon calculation factor today. And since there is a variety of conversion protocols to choose from – TRACI, WRI/WBCSD, Climate Registry etc – it is not currently possible to get a definitive carbon number.
So, what are you to do? Gil Friend has collected many online calculators today here. It is a very good list if you are looking for what is available today and also takes advantage of social media and asks you to rank the calculators you try. I would recommend the free online calculators only to give you an idea of what your carbon footprint may be. If you really are interested in developing a baseline and report on your carbon, you need to understand more the underlying methodology of the conversion factors and choose those that are more reflective of your regional location and/or product type. And generally those are not free today. Several good sources are in the links section of my site where you can find out more about these carbon calculators.