So generally speaking when you buy a book about 10% of the sale price will go to the author (although most of that will likely just go against the advance the author has already been paid).

When you borrow a book then in addition to the author getting that 10% when the library bought the book they also get library royalties known as Public Lending Right (PLR). PLR isn’t very much, in the UK it just increased to 30p a loan from a rate of 11p it had sat at for many many years. But it’s not nothing. (altho yes it also generally gets swallowed up by the advance).

Even so if you think the average price of a paperback is, what, £8? So the author royalty on a new sale will be about 80p. So one sale is worth about three library loans. So yeah the author would probably rather the sale if that was the choice but it often isn’t is it? Often if you didn’t borrow the book you wouldn’t buy it. In fact you’d have to buy one book for every three you borrow for the odds to be more in their favour if you walk into a book shop than a library, and I think for most people that’s not the ratio.

Here’s another one that some people don’t know, although it applies more to non fiction: authors also get royalties each time their book is photocopied. However because these royalties are very very small and very very hard to calculate it is not possible to directly enforce royalty claims. Instead what happens is libraries, schools, universities and other public institutions where a lot of book photocopying takes place have to buy a licence to provide that service. There are a number of different licence sellers of which CLA is the most common. Then those licence sellers conduct random sampling and based on that random sample data they allocate the profits they made from selling those licences among the authors who are members of their schemes in proportion to the number of times they estimate their book was photocopied. TBH I’ve never heard of an author making more than money for a couple of beers that way, but every little heps.