What constitutes a "bestseller"?

Surely to be "best", it needs to be better than everything else in it's category, otherwise it would only be a "betterseller", "averageseller" or even "poorseller" (spare a thought for the "worstseller").

But I keep coming across respectable websites for reasonable books from reputable publishers claiming bestseller status for books that I've never heard of and doubt many would give a damn about even if they were astonishing.

So... A riddle, please fill in the blanks;

"Bestseller" status is to actual sales ranking as ____ is to ____.

Cynical Moon-unit of Ygarthruar 9

The usual criteria is that it was in the Sunday Times top ten bestseller list, which is based on Nielsen book data.

If it was a number one bestseller then they usually say that. Bestseller means somewhere 2-10.

These are divided into categories (HB fiction, HB non-fiction, PB fiction, PB non-fiction, HB childrens, PB childrens, Manuals) and sometimes broken down further in other publications (eg you might find a Crime list one week). There are also other lists in other papers which vary slightly in their criteria. But in general "bestseller" means it was 1/2-10 within its own hb/pb category and "number one bestseller" means specifically that. It doesn't depend on any specific number of titles sold, so something could be number 1 with X number of copies in January, and yet a book that sold the exact same amount in September might not even make the list.

"International bestseller" means that it has appeared on a bestseller list in other countries (usually more than one other country) - but not necessarily this one.

In the US the NY Times is the gold standard so you will sometimes see that specified in the description.

Also just as an fyi, Nielsen figures are currently based solely on physical copies, so ebook heavy categories (crime, mainly) are arguably at a disadvantage. I think there are plans to address this.

HTH!

<Added>

that's not half to ten btw, that's me being inept. It was meant to mean "it's between one/two and ten"

HTH

Yes, very clear, and explains how there can be quite so many of them...
One site I found claimed all of his dozen or so books were bestsellers, for example.

so something could be number 1 with X number of copies in January, and yet a book that sold the exact same amount in September might not even make the list.

This is also important. I mean, bestseller is still good, but not much of a measure of anything. A "nice-to-have" rather than an essential for success.
G