Traditional Japanese katana swords are typically made using a process called "forging and folding," where multiple layers of steel are combined to create a blade with a distinct grain pattern. The number of layers can vary depending on the specific swordsmith and the desired characteristics of the katana, but it often ranges from around 8 to 16 layers.

During the forging process, the swordsmith starts with a stack of alternating layers of high-carbon steel and low-carbon steel, typically in the form of thin plates or bars. The stack is then heated, hammered, and folded multiple times to create a layered structure. This folding and hammering process serves several purposes, including removing impurities, improving the steel's consistency, and creating a fine grain structure.

With each fold, the number of layers doubles. For example, starting with 8 layers will result in 16 layers after the first fold, 32 layers after the second fold, and so on. This repeated folding and layering contribute to the unique grain pattern, known as "hada," seen on the surface of the finished katana blade.

It's important to note that the number of layers does not necessarily indicate the quality or performance of a katana. The skill and technique of the swordsmith, the quality of the steel used, and the overall craftsmanship are more significant factors in determining the quality and characteristics of the katana blade.