US size 20 in women's dresses is UK size 24. This is equivalent to the XXL international size. This dress size has a bust of 120-125 cm (47-49 inches), a waist of 103-108 cm (40-42.5 inches), and a hips size of 123-128 cm (48-50 inches).
So, if you're a size 24 waist, you'll be an AUS size 6 because 2+4=6.
So a 24 is equivalent to a size 0.
Now that you've measured your waist circumference you need to know what it means. To have your best chance at maintaining good health, you should aim for: Men should have a waist circumference of 40 inches or less. Women should have a waist circumference of 35 inches or less.
For a female, a 24-inch waist is smaller than 99% of women, even among fit people. So indeed, it's a rare feat to achieve such a tiny waist measurement. Still, that's not to say it's impossible. A 24-inch waist could be attainable if you have a naturally petite frame, eat a healthy diet, and exercise regularly.
What Is 2XL or 3XL? Traditionally, 2XL and 3XL were intended to be shorthand for XXL and XXXL. However, with the increasing availability of plus sizing, these abbreviations led to confusion and are no longer used here at Outdoor Research.
The cut of the garment is the same it's just done "on a larger scale" no pun intended. A 2XL garment is cut differently. In fact, it's half a size bigger than an XXL. The cut of the garment is also different.