Inclusive sizing is one of the biggest trends in retail, leaving fashion brands scrambling to extend women's clothing lines well beyond the traditional offerings.

• The brass ring is to offer sizes 00-40 — not just "plus" sizes 16-26 — in everything from jeans and lingerie to formalwear.

Why it matters: As the average American woman has become larger — and younger women embrace body positivity and show off their curves on TikTok — the term "plus size" and its negative connotations are rapidly being banished.

• The average U.S. woman wears a size 16 or 18, according a 2016 study still considered the industry benchmark.
• But 42% of American adults "gained more weight than they intended" during the pandemic, according to a survey by the American Psychological Association and the Harris Poll — and now they're shopping for larger sizes.

Driving the news: Major retailers like Nordstrom, Target, Kohl's and Anthropologie have introduced inclusive sizing options in a steady march over the last three years.

• They're competing with brands formed specifically to serve this market, such as Universal Standard, Rihanna's Savage X Fenty lingerie and Yitty (Lizzo's shapewear collaboration with Fabletics).
• They're trying to get the fit right for larger bodies, with new designs that don't just scale up patterns used for the average size 8.
• And they're being goaded by younger consumers who demand the latest fashions in larger sizes and worship social media stars who wear them, like Remi Bader.

Long relegated to stretchy "athleisure" clothing, inclusive sizing is now "a big driver in intimates," says Juliana Prather, chief marketing officer at Edited, a retail data analytics company. "It's becoming something to talk about in luxury."

• Women want to go shopping with friends without having to slink into a separate plus-size department stocked with hideous floral muumuus.
• Younger women "are wearing whatever they want, whatever size they are — they're having a good time," Prather said.
• "If you're J. Crew, The Gap, a large retailer, you've got to figure out what to do, what steps you're going to take."

By the numbers: The market for larger-sized women's apparel is growing faster than the total women's clothing market — and gaining share, according to a Coresight Research report.

• Sales were $34.3 billion in 2021 — up 21.2% from 2020 — and expected to grow 7.6% this year.

Yes, but: It's historically been difficult to profitably serve the extended-size market, in part because it's tricky to manage inventory in so many sizes and styles.

• Old Navy made a splashy debut of inclusive sizing last year in a campaign called "Bodequality" — only to see it backfire.
• The company pulled back, saying it had "not seen the expected demand for extended-size products in our stores."
• Loft dropped extended sizes last year, citing "continued business challenges" from the pandemic.
• Larger clothes are more expensive to manufacture, and when retailers pass the cost on to consumers, they're accused of levying a "fat tax."

The other side: Menswear is a laggard in inclusive sizing — not because men aren't getting bigger, but perhaps because they shop less, or because sales of men's plus-size fashions have declined.

• Brands like Ralph Lauren, Lee and Tommy Bahama have "big and tall" options, but there isn't the crush of interest and activity that there is on the women's side.

What's next: Retail experts predict that more womenswear and menswear brands will learn how to get inclusive sizing right — and will add adaptive apparel, for people with disabilities and the elderly, and gender-neutral clothing.