Santino Fontana is no stranger to competition. He’s been up for plenty of awards, including a Tony this year for his starring role in “Tootsie.”

But he didn’t expect his wife, actress Jessica Hershberg, to compete with him, too.

“When we started all the transformation stuff, she’d ask, ‘What’s your waist size?’ ” he tells The Post. As if he could possibly best his shapely wife in THAT arena.

As far as that “transformation stuff” goes, he’s sure the bra he wears as Dorothy Michaels — Michael Dorsey’s better half — isn’t the 34B Dustin Hoffman sported in the 1982 movie.

“I’m definitely bigger than that!” Fontana says. “I have a big rib cage.” So big, in fact, that when costume designer William Ivey Long came in for a costume fitting, he put a finger on Fontana’s ribs, just to make sure it was really all him in there.

“Yes, that’s me!” the 37-year-old told him. And so Dorothy’s dresses rely on boning, zippers and elastic to cut a credible figure, along with butt pads and what Fontana calls “hardcore Spanx.” He also spends 90 minutes on show days shaving his face and chest, and once a week tackles his arms and legs.

So much for Dorothy’s looks: Getting her voice was even harder. The movie’s characters didn’t sing, but the Broadway ones do.

Fans of TV’s “Crazy Ex-Girlfriend,” on which he played the lead’s affable male friend, Greg, may recall Fontana’s natural voice as a resonant tenor verging on a baritone. To make a credible soprano, his voice teacher, Joan Lader, had him sing Dorothy’s first song in every key, up and down the scale. The next challenge: finding a sound he liked, and one he could produce eight times a week, in Dorothy’s Southern accent.

That accent was a no-brainer, he says, because Dorothy being Southern was one thing everyone recalls from the movie. (That, her red dress — and the fact that she is really a he.) Still, Fontana couldn’t resist doing one reading in which Dorothy hailed from . . . Minnesota.

“It was ‘Oh, ya know, oh yah, you betcha,’ ” says Fontana, who fondly remembers his college days in Minneapolis. “Dorothy’s kind and sweet, so I guess that’s why I thought of Minnesota.” In the end, he and the show’s creators agreed to stick with the South.

And yet it was a gal from Queens who really shaped Broadway’s Dorothy. Fontana had already been cast in “Tootsie” when he stepped into “Hello, Dolly!” for two months opposite Bernadette Peters. “I’d go to her hair and costume fittings and say, ‘Guys, I want to look like Bernadette, another Italian woman. She looks amazing!”

He even asked Peters for a wig consult, printing out a Website showing his face under different hairdos. “She’d write above the ones she liked, ‘Pretty girl,’ and above the ones she didn’t like, ‘NOT so pretty girl.’ She’s been lovely.”

So is Dorothy. When Fontana talks about her — the way this fictional character stands up for other people, and does everything with love — it’s clear he’s smitten. And he wants everyone else to love her, too. With some exceptions:

“My wife asked me if I’d hang out with her as Dorothy at home. Not going to happen!”