US standard clothing sizes for women were originally developed from statistical data in the 1940s–1950s. At that time, they were similar in concept to the EN 13402 European clothing size standard, although individual manufacturers have always deviated from them, sometimes significantly.
However, as a result of various cultural pressures, most notably vanity sizing, North American clothing sizes have drifted substantially away from this standard over time, and now have very little connection to it. Instead, they now follow the more loosely defined standards known as US catalog sizes.
Men's standard sizes were probably developed first during the American Revolutionary War, and they were in regular use by the American army during the War of 1812 for ready-made uniforms (Felsenthal 2012). These were based on the chest measurement, with other measurements being assumed to be either proportional (the circumference of the neck, waist, hips, and thighs) or easily altered (length of the inseam) (Felsenthal 2012).
As this was largely successful in men, the same approach was attempted in the early 20th century for women using the bust as the sole measurement (Felsenthal 2012). However, this proved unsuccessful because women's bodies have far more variety in shape. The hourglass figure is frequently used as an industry standard, but only 8% of women have this body shape (Felsenthal 2012). A woman with an hourglass figure and a woman with an apple-shaped figure who have the same bust size will not have the same waist or hip sizes.
This was a significant problem for mail-order companies, and several attempts at predictable, standard sizing were made (Felsenthal 2012). In the 1940s, the statisticians Ruth O'Brien and William Shelton received a Works Progress Administration grant to conduct the most ambitious effort to solve this problem. Their team measured almost 15,000 women across the US. After discovering the complex diversity of women's actual sizes, which produced five to seven different body shapes, they proposed a three-part sizing system. Each size would be the combination of a single number, representing an upper body measurement, plus an indicator for height (short, regular, and long) and an indication for girth (slim, regular, and stout). The various combinations of height and girth resulted in nine different sizes for each numerical upper-body measurement, which was highly impractical for manufacturing (Felsenthal 2012).
As a result, O'Brien and Shelton's work was rejected. In 1958, the National Bureau of Standards invented a new sizing system, based on the hourglass figure and using only the bust size to create an arbitrary standard of sizes ranging from 8 to 38, with an indication for height (short, regular, and tall) and lower-body girth (plus or minus). The resulting commercial standard was not widely popular, and was declared voluntary in 1970 and withdrawn entirely in 1983. In 1995, ASTM International published its own voluntary standard, which has been revised since then (Felsenthal 2012). It has not been widely adopted.
Women’s sizes are divided into various types, depending on height. These charts give an indication of size only and are by no means exact as they vary from manufacturer to manufacturer, sometimes by a full inch up and down.
There are multiple size types, designed to fit somewhat different body shapes. Variations include the height of the person's torso (known as back length), whether the bust, waist, and hips are straighter (characteristic of teenagers) or curvier (like many adult women), and whether the bust is higher or lower (characteristic of younger and older women, respectively). These categories include:
The most common size category. For women of about average height (5'4") with an average bust height and an hourglass figure. Dress sizes may be given as girth at the bust in inches (e.g., 36), but even-numbered sizes from 2 to 16 are more common. Categorical sizes range from XS (extra-small) to XL (extra-large).
For short women with higher busts and fairly straight bodies. Junior sizes are commonly given as odd-numbered sizes from 1 to 15, which correspond to the next number up in misses' sizes.
Women's sizes or plus sizes
For larger, curvier women of average height, sometimes with lower bust lines. Like misses' sizes, the sizes may be given as a dress size based on the bust measurement, but they are usually given as even-numbered sizes from 18 up. Categorical sizes usually range from 1X (similar to extra-large, but with slightly different proportions compared to the misses' size) up.
For short women with average busts and more hourglass body shapes. Sizes follow the misses' standard and are marked with a P, as in 10P.
For very short women with average busts and fairly straight bodies. Size may be denoted as "5JP" or as "5P".
For larger, curvier, shorter women, sometimes with lower bust lines. Sizes are marked the same as women's with a P, as in 20P.
For short women with high busts and fairly straight bodies.
For taller women (usually 5'8" or above), usually with a proportionately average bust height and an hourglass figure. Sizes are usually written with the corresponding misses' size and a T to indicate tall, as in "10T".
For short women with lower busts and more hourglass body shapes. Sizes are written with a ½, as in "10½".
Companies who publish catalogs may provide the measurements for their sizes, which may vary even among different styles of the same type of garment. The sizes seen in catalogs generally have roughly the following measurements:
Catalog misses' sizes: 5'5"-5'6" (165–168 cm) tall, average bust, average back
With the average American woman's height (20 years and older) at about 63.8" or approximately 5'4" (162.1 cm) (Department of Health 2012), both standard and catalog size ranges attempt to address a variety of weights / builds as well as providing for the "shorter-than-average" height woman with "petite" and "half-sizes". However "taller-than-average" women may find their size-height addressed by manufacturers less frequently, and may often find themselves facing issues of slightly too short pant legs and sleeve cuffs, as well as waist lengths.