Bosa said he has wanted to switch back to his college number for some time but waited until this season due to financial considerations, with the Chargers moving to powder-blue uniforms as the team's primary home uniform for the upcoming year.
Running back Melvin Gordon also will switch from No. 28 to his college No. 25 at Wisconsin this season.
"They told me it would be $500,000 if I wanted to do it last year," Bosa said. "So I was like, 'Eh, I think I can wait one more year.' The free change was much better than that."
Bosa and his younger brother Nick will now both wear No. 97, the same jersey number worn in the NFL by their father, John Bosa.
Joey Bosa said it's nice to have his brother, who was selected No. 2 overall by the San Francisco 49ers in this year's NFL draft, on the West Coast.
"We've been wearing that through high school and college," Bosa said about No. 97. "I mean, my brother wore my exact jersey through high school. Probably not through college, but the same number. It's just a cool tradition. I'd like to keep it going."
A lean-looking Bosa also said he feels healthy this offseason, successfully managing to avoid a Lisfranc-type surgery after suffering a bruised left foot during training camp last year that forced him to miss the first nine regular-season games.
"As expected, I deal with soreness here and there, but there's been nothing limiting me -- no movement or anything," Bosa said. "I'm as fast and strong as I've ever been in my life. It's just about some little things like my hands and stuff, but as a defensive lineman, you're going to deal with that stuff."