How does the ECTS ABCD etc grades compare to the American ones?
Would I in particular be right in saying that the European B is worth more than the American B?
How does the ECTS ABCD etc grades compare to the American ones?
Would I in particular be right in saying that the European B is worth more than the American B?
They don't compare at all.
With ECTS, grades correspond to relative position of the student for a given course. For example, A is for the top 10%, B for the next 25%, and so on. These percentages are out of passing students – even E is a passing grade, by definition. Students who fail get F or FX depending on the severity of failure. This is based on statistical data for that year and previous years, so that if in some year many students perform exceptionally well (or bad), then that should be taken into account, in theory.
(Converting grades is not an easy task. In my understanding the letter grades are not used anymore, rather the administration will actually convert the local grade into a foreign grade. There is an example in Annex B of the ECTS guide from 2015.)
See this page for more information: http://ec.europa.eu/education/ects/users-guide/grade-distribution_en.htm
Grades in the US are completely different. First, the passing grade is often C, not E, therefore the distribution of grades will obviously be different. From what I understand (correct me if I am wrong), anything lower than a B+ is quite bad for undergrad courses.
Moreover grades are not necessarily correlated with the student's standing relative to other students, unless the grading is done on a curve (which an outsider does not know) – it's possible for everyone to get an A, which is by definition impossible with ECTS grading.
How does the ECTS ABCD etc grades compare to the American ones?
You cannot compare them. Comparing grades in anything else than standardized tests doesn't make much sense. And sometimes it's even hard to compare results of different runs of a standardized test if the questions change.
You might compare grades given by the same professor on the same subject, but even comparing grades given by different professors on the same subject at the same school often doesn't work.
Would I in particular be right in saying that the European B is worth more than the American B?
I don't have any hard data on this but in general this might actually be the case, at least in my experience. In many european countries on many european universities things like grading on a curve doesn't exist and grade inflation isn't nearly as bad as in the US. For example in the Netherlands getting 8/10 is already very good and you could definitely compare that in most cases to a US A. 9/10 is very rare and 10/10 doesn't happen very often. But keep in mind, even here in Europe there are big differences in different countries.
Also, as deviantfan pointed out in a comment, ECTS are just a measure of how much time a course needs, not how difficult it is.