The thickness of a katana handle, known as the tsuka, can vary depending on the specific sword and the preferences of the swordsmith or owner. However, on average, the thickness of a katana handle ranges from approximately 2.5 to 3.5 centimeters (about 1 to 1.4 inches) in diameter.

The tsuka of a katana is designed to be grasped comfortably and securely by the hand. It typically tapers slightly from the base to the top, where the guard (tsuba) is located. This tapering shape allows for a more ergonomic grip and facilitates proper handling and control of the sword during use.

It's worth noting that the precise dimensions of the tsuka can vary depending on factors such as the size of the swordsmith's hands, the desired balance of the katana, and the specific style or school of swordsmanship. Different swordsmiths and traditions may have their own preferences in terms of handle thickness and shape.

Additionally, the tsuka is often wrapped with a layer of silk or cotton cord, known as the ito, which further adds to the overall thickness and grip of the handle. The ito wrapping provides additional comfort, traction, and insulation for the hand.

In summary, the thickness of a katana handle, the tsuka, can range from approximately 2.5 to 3.5 centimeters (1 to 1.4 inches) in diameter, but the specific dimensions may vary based on the individual sword, swordsmith, and the desired balance and feel of the weapon.