know (something) backwards and forwards

To be extremely familiar with a particular subject, field, or piece of writing, film, music, etc. I've read this book so many times, I know it backwards and forwards. You should ask Samantha about the issue—she knows car engines backwards and forwards.

know something backwards

mainly BRITISH or

know something backwards and forwards

mainly AMERICAN

If you know a subject backwards, you know a lot about it. I thoroughly enjoy lecturing and know my subject backwards. He will be very much in demand. He knows the business backwards. They know company personnel policy backwards and forwards.

know something backwards

be entirely familiar with something.

1991 William Trevor Reading Turgenev People who lived in the town knew it backwards.