Go with 12-53 if you want a safe bet.

I don’t know what Julia Jacklin’s rhythm guitarist actually uses — that information isn’t published anywhere obvious. But for an acoustic that needs to project in a band mix while still letting you bend strings, 12-53 is the standard compromise.

Heavier strings (13-56) project better but fight you on bends. Lighter (11-52) bend easy but can get swallowed by a drummer. 12-53 gives you enough tension for volume and enough slack for expressive playing. Most rhythm players in folk-rock settle here for exactly that reason.

If you’re tuning down a half-step or full step, you can drop to 11-52 and keep the same feel. Your guitar’s scale length matters too — shorter scale feels looser, so you might prefer 13s on a parlor.

But if you’re just trying to get in the ballpark, buy a set of 12-53s and adjust from there.

You’ll spend more time playing and less time fighting your strings.