The standard length of a traditional Japanese katana is around 2.5 to 3 shaku, which is approximately 75 to 90 centimeters or 29.5 to 35.4 inches. However, the exact length can vary based on personal preferences, the style of swordsmanship practiced, and the physical attributes of the individual using the katana.

When selecting a katana length, it is important to consider factors such as your height, arm length, and the intended use of the sword. Here are a few general guidelines to help determine an appropriate katana length:

1. Personal comfort and handling: The length should feel comfortable and balanced in your hands. It should allow you to execute proper sword techniques and maintain control during strikes and defensive maneuvers. It's recommended to try different lengths to find one that feels most natural and suits your body proportions.
2. Functional use and intended purpose: Consider the primary use of the katana. If you plan to practice martial arts like Kendo or Kenjutsu, it's best to consult with an instructor who can provide guidance on the appropriate length for your training and style. If the katana is primarily for display or collection purposes, the length can be chosen based on historical accuracy or personal aesthetic preferences.
3. Body proportions and physical attributes: Your height, arm length, and overall physical build can influence the ideal katana length for you. Longer arms may benefit from a slightly longer blade, while shorter arms may find a slightly shorter blade more comfortable to handle. It's important to find a length that allows you to maintain proper form and control without feeling overly cumbersome or restrictive.

Remember that katana length is a matter of personal preference and should be chosen based on your specific needs and considerations. It is always recommended to consult with a knowledgeable instructor, experienced swordsmith, or reputable dealer who can provide guidance tailored to your situation and requirements.