know (something) like the back of (one's) hand

know (something) like the back of (one's) hand

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 like the back of my hand. You should ask Samantha for directions—she knows this town like the back of her hand.
See also: back, hand, know, like, of