The tsuba is the handguard of a Japanese sword, including the katana. The size of a katana tsuba can vary, but typically it has a diameter of around 3 to 4 inches (7.6 to 10.2 centimeters).

The tsuba is an essential component of a katana as it provides protection for the hand and serves as a counterbalance to the blade. It is usually made of metal, such as iron or brass, and is often decorated with intricate designs or motifs.

While the approximate diameter of a katana tsuba is 3 to 4 inches, it's important to note that the size can vary between individual swords and the preferences of the sword owner or craftsman.

Some tsuba may be slightly larger or smaller depending on the specific design and historical period.

In summary, the diameter of a katana tsuba typically falls within the range of 3 to 4 inches (7.6 to 10.2 centimeters), but the exact size can vary based on the individual sword and the preferences of the owner or craftsman.