The Bianconeri confirmed the amount, adding they would owe the Gunners an additional €3.1 million if certain bonuses are achieved.
Szczesny - who kept the most clean sheets in Serie A last season during his loan spell at Roma - signed a four-year contract with the Old Lady.
He's the club's second major signing of the summer window - even if he's not expected to make an immediate impact.
That's because Buffon has said he intends to retire after the 2018 World Cup, meaning Szczesny must accept being the 39-year-old's backup next season.
Not that it seems to faze the Polish shot-stopper.
"When you join this club, it's Juventus that chooses you, not the other way around," Szczesny said at a press conference Wednesday. "I've been waiting to come here for a long time, so I'm delighted.
"I feel lucky because I'm not the kind of person that feels pressure. I think I'm capable of playing at the highest level, so I'm not worried. I'm ready to play whenever I'm needed. I'm available."
Szczesny spent the past two seasons on loan at Roma, making 72 appearances in Serie A and helping the Giallorossi achieve a club-record 87 points during the 2016-17 term.