Initially there was no concept of the types of paper size and everyone pretty much wrote on papyrus and the barks of trees but as time developed and modern technology introduced us to the ability to use paper leaves to manufacture paper, different types of paper size were discovered. Different companies, countries and people use different types of paper size though. Everyone knows of the various types of size because these are used around the world for different reasons nowadays. There are even types of paper size for envelopes and such like.
Loose sizes are one of the many types of paper size you would find and see in North America. Though other countries tend not to use these much, it is commonly used in the US and is ¼th the size of the imperial types of paper size which means that they are somewhat shorter than these. Initially they were used in order to make books because it was felt that it was easier to bind papers that came in these types of paper size but eventually, Ronald Reagen took control and made it a necessity for the US government to go for the letter size which was shorter. These types of paper size are still used in some countries though.
Then, there are those types of paper size that are known as the A4 size paper sizes which are pretty standard in countries in Asia. If you go to Pakistan, India, Bangladesh and Malaysia, for example, you would see that these types of paper size are very widely used here and most books, textbooks, copies, sheets and such like make use of these types of paper size. This is also used in the US. These types of paper size are the most common and widely used ones in the world today.
There are also the A1 types of paper size which are quite large and have to be rolled and carried around by anyone using these. You would not find just about anyone making use of these types of paper size because they tend to be a bit too big. Architects, engineers, industrialists, artists and people who make posters use these types of paper size because, for them, this size is more convenient. They can draw on these easily and change anything that needs to be changed on the paper, there and then as well.
These are some of the many types of paper size you would come across and these are mostly used ordinarily by most people. Other types of paper size may be used for other purposes and projects. By way of example, some magazine publishers go for different types of paper size and likewise, some publishers use smaller types of paper size when they publish books and such like. Then, there are those people who make canvases of different sizes for art students and artists and so there are different types of paper size for different purposes. The prices may vary as per the paper size.