carboncount turns an activity into an estimate of the CO2 equivalent it produced. Pick an activity, say how much of it there was, and it lands in a table alongside the emission factor used and the total. The factors come from DEFRA, Our World in Data and other published sources, every one of them cited. Nothing is stored and nothing is tracked.
The calculator itself needs JavaScript, but these pages do not: Methodology sets out where every factor comes from and how the arithmetic works, and Support explains how to support the project.