The standard clothing that most stores have focused on in recent years fits fewer and fewer people. And as retailers search for ways to invigorate sales, plus size is one of the few categories where there is growth. The plus-size market increased 1.4 percent while overall women’s apparel declined 0.8 percent in the 12 months leading up to April 2010 versus the same period a year earlier, the most recent figures available, according to NPD Group, a market research firm.

“It just makes business sense,” said Ms. DeVoe, who founded “Full-Figured Fashion Week” last year to press mainstream retailers to embrace bigger sizes. “I’ve been told several times that no one fantasizes about being a plus-size woman, and that’s probably true, but the fact remains that you have to work with what you have.”

That is not always so easy for retailers venturing into the world of larger shoppers. Some bigger women do not like to try on clothes in the same fitting rooms as smaller women. Plus-size stocks take up valuable storage space, and not everyone is big in the same way, meaning stores cannot count on, say, a size 16 dress fitting most 180-pound women — one might have a larger torso, another big thighs and another wider hips.

“There are variations not only in the frame, but if you’re looking at larger women, you’re also looking at the way fat deposits are arranged around the body,” said Susan Ashdown, a professor at Cornell who studies body shape and clothing fit by creating a three-dimensional scan of a person’s almost-nude body.

Plus-size clothes, which now generally begin at size 14, have been around for at least 90 years, since a Lithuanian immigrant, Lena Bryant (her name was later misspelled as “Lane” on a business form), turned a maternity-wear business into a line for stout women in the 1920s. There have been several efforts to make plus-size clothes more available, but, as the name of the 1980s-era plus-size chain The Forgotten Woman suggested, larger women have usually been relegated to stand-alone boutiques stocked with shapeless purple caftans.