I’ve always calculated series cardinality per measurement, honestly, that’s the only way I’ve seen it so far. (this post about cardinality calculation says the same for InfluxDb v2)
This is the definition of Series: A logical grouping of data defined by shared measurement, tag set, and field key.
if you have dependent/related tags the plain/simple multiplication will get you an over-estimate of cardinality (see here)
The doc link you shared isn’t clear enough about this, therefore I’ll ask @Anaisdg if she can have a look at it too. It might be worth updating it in case that’s misleading
