Shopping for clothes is like going on a fishing expedition for Thais Austin. On a recent excursion for a pair of black pants, she tried on at least 10 pairs, in sizes ranging from 4 to 10, before settling on a size 6.

"It's a process of elimination, casting a wide net and bringing it in," said the 42-year-old Texas resident, noting that she has learned to let go of her numerical "ego size" (a 4) and focus on how the clothes fit. "At this point, I can't really buy by size because there are so many variables."

It's long been the bane of a shopper's existence: finding clothing that actually fits. The numbers on the labels increasingly are meaningless, as designers and retailers play to vanity and their own customer demographics in determining the length of an inseam and width of a waistline.

But a coterie of clothing retailers and manufacturers are seeking to bring more predictability and precision to clothes sizes. They are sponsoring the first-ever American "sizing census," called "SizeUSA," to determine the shape of American consumers -- everything from neck circumference to waist/hip ratios.

The project is the brainchild of TC2, a group in Cary, N.C., that has developed computerized body scanners to take detailed three-dimensional measurements. It plans to use the technology to analyze the frames of 10,000 male and female volunteers by this summer.

The federal government has provided a grant, and major retailers and clothing manufacturers -- including Federated Department Stores, Target Corp. and Liz Claiborne Inc. -- are sponsoring the survey with additional financing or donations of gift cards to help recruit participants.

A modern study of the size and shape of Americans hasn't been done before, TC2 executives say. In fact, the clothing sizes used by many apparel companies are measurements that originally were derived from U.S. military and government research conducted back in the 1940s, when Americans were more svelte as a population and not as ethnically diverse.

While apparel manufacturers refer to these government-issued body measurement tables, there is no law or regulation requiring them to strictly adhere to the charts. Each company can subjectively interpret how big and wide a size 6 should be and, as a result, today's sizes are all over the map.

There's a pervasiveness of "vanity sizing," whereby a woman who is a true size 6 might find herself comfortably fitting into a size 2. (The problem is more pronounced with women's clothing than men's.) And many companies have developed their own in-house sizing scales to fit the frames of people who they think are their core customers.

For instance, Chico's, a 400-store chain that markets mostly to women between the ages of 35 and 55, has sizes that run from 0 to 3 -- 3 being equivalent to a standard 14 to 16.

"Wouldn't you rather wear a 2 1/2 than a 14?" asked Patricia Murphy, Chico's executive vice president and chief merchandising officer.

Abercrombie & Fitch, which touts its "classic American style," targets the 18- to college-age generation with extremely casual, body-conscious clothes. Its smallest women's size is a 00, which has a 23-inch waist and 33-inch hip.

"They need to sell some cribs and bibs there because their clothes look like they were made for babies," 17-year-old Brigette Poniewaz said about Hollister, a clothing-store chain that is part of the Abercrombie corporate family and is targeted at teen-agers.

To see how varied sizing can be, we purchased 24 garments, each labeled size 8, from 10 different manufacturers. (For the European clothes, we purchased the equivalent, size 42.)

While some garments truly were ready to wear, others needed expert tailoring to pick up the slack or were plainly too small and needed to be a size larger. An Ellen Tracy dress looked fantastic in the front but was baggy in the lower back.

A Moschino dress from Italy was too tight. And our professional model was busting out of a size 8 ensemble from Swedish retailer H&M.

"We're known for a little more chic, trendy fit," said Cindy Azzarello, head of quality control for H&M in the U.S. "If you make a trendy style and you make it relaxed and goofy-looking, you've changed the whole look."

A Moschino executive said that Italian clothes are cut smaller than American apparel because Italians are generally smaller than Americans and prefer a more fitted look.

It's no secret that Americans are getting chunkier. Their growing waistlines have implications for the apparel, automotive and furniture industries, which all need to design products that can both fit and flatter their customer base.