Giving the new Small99 carbon calculator a go, because I'm fascinated by different models and the balance between simplicity and accuracy.
The process is very simple, although the results are... vague. Looking into it, the methodology is pretty opaque - "The magic is our IP, so we can’t share full details".
Should we demand that carbon calculators show their workings, and avoid those that don't?
The calculator: https://measure.small99.co.uk/
The methodology: https://measure.small99.co.uk/about/