At 5 feet 8 inches, with a slender build, Peter Manning says that finding clothes for his proportions has been a challenge his entire adult life.

“I’ve never bought a pair of pants or a jacket that fits me right,” said Mr. Manning, 46, a former Broadway producer. “Tailoring them or looking sloppy is the way I’ve always had to go.”

Frustrated with his limited options, Mr. Manning started a clothing collection bearing his name in mid-2012 for men like him or smaller (which would be around 25 percent of all American men, according to the most recent data from the Centers for Disease Control and Prevention), selling it exclusively on his website petermanningnyc.com.

On a recent winter afternoon, the energetic Mr. Manning bounced around the conference room in his offices near Union Square, showing off the line of everyday T-shirts, jeans, blazers, cotton and wool sweaters and khakis, which cost $28 to $800.