To be sure, sizing is an inexact science. Women's sizes were developed in the 1920s as catalogues became popular and ready-to-wear clothing replaced tailor made or self-sewn items.
But while a system of men's standard sizing based on chest sizes in the Army had worked well, a similar attempt to base women's sizes on bust measurements wasn't as reliable. Women's bust sizes are more variable.
In the 1930s, retailers began adopting even-numbered sizes commonly ranging from 14 to 24, says Alaina Zulli, a dressmaker who studies costume history. But those sizes bore little resemblance to those used today — a size 24 back then, for instance, would be a size 14 today — so the issues of not having enough plus-size fashions likely was not as pronounced.
The sizes stayed the same but the numbers decreased gradually, Zulli says, about 1 size a decade. This is known as "vanity sizing" because it gives women the allusion that they're fitting into a smaller size.
Women's sizes, which today range from 0 to 24 but vary from store to store, haven't evolved much for decades. And for the most part, neither have the range of plus-size fashions.
As a result, the amount spent on women's plus-size clothing annually has only risen by one percentage point to 9 percent since 2011, the furthest back plus-size data available from research firm NPD Group.
"If the offering becomes stronger, women will spend more," says Alison Levy, a retail strategist at consulting firm Kurt Salmon. "There's a significant dollar opportunity in what is currently a very depressed apparel segment that retailers should be looking to exploit."
Some retailers have started to do just that. H&M, a European-based retailer that sells trendy clothing in the U.S. equivalent of sizes 1 through 16, last summer featured plus-size model Jennie Runk, who is a size 12 or 14, in its swimsuit ads. "Our aim is not to convey a certain message or show an ideal, but to have a campaign which can illustrate the collection in an inspiring and clear way," said Andrea Roos, an H&M spokeswoman.