All about clothing size conversion!
Take into account that clothes sizes vary from region to region. And if you are buying something imported from the UK in the USA then there will be different sizes. The reason for this is the difference in build between races, people and nations because of wealth, eating issues, etc. Westerners will have larger builds than Asians and the various clothes around the world reflect that. It is the size of the people wearing the clothes that are what usually determines the size system. In women's clothes size for underwear, one can expect that bra sizes would have different systems of measurements based on the average and current size of female bust sizes in that particular region. There are cloths size standards, such as the ISO standard 3635, but the problem is that not all countries and manufacturers follow the standard. Add to this that every region or continent has different clothing size standards and clothing manufacturers are not required to adhere to them. In the US, for example, there is US standard but it's not mandatory for clothing companies to observe them.
The difference in sizes is also reflected in genders. Women's clothes sizes are different to men's - same for boys and girls.
One of the things that make buying clothes difficult is the variety of clothing sizes presented by different regions and different clothes manufacturers. What this means is that a women clothes size of 6 in the US won't be the same size in the UK. This can make choosing clothes of the right fit confusing and even frustrating.
Another reason for the different clothes size standards is the difference of build between different races and peoples. Naturally, westerners would have larger builds and bodies compared to Asians. Thus, there would be different standards on what is small, large or medium. There would be different neck, torso and waist sizes for different regions. Also, it's the size of the people wearing the clothes that are what usually determines the size system. In women's clothes size for underwear, one can expect that bra sizes would have different systems of measurements based on the average and current size of female bust sizes in that particular region.
There are cloths size standards, such as the ISO standard 3635, but the problem is that not all countries and manufacturers follow the standard. Add to this that every region or continent has different clothing size standards and clothing manufacturers are not required to adhere to them. In the US, for example, there is US standard but it's not mandatory for clothing companies to observe them. The nearest thing to standardization is the EN 13402 standard, the European clothing sizing standard that will be enforced throughout its member nations. That would be welcome news for people who travel around in Europe.
One way to overcome this confusion and profusion of cloths size standards is by having conversion charts at the stores. You can also check online beforehand for the size of your dress and its equivalent in the region that you're in. That can lessen the pain of dealing with different clothes sizes if you do a bit of research on your end. We also have a conversion table here to help you out a bit with your clothes selection.
Clothes size table: (info from http://www.thetipsbank.com/clothessize.htm)