The thickness of a jian, which is a traditional Chinese straight sword, can vary depending on the specific sword and the preferences of the swordsmith or owner. However, on average, the thickness of a jian blade ranges from approximately 4 to 6 millimeters (0.16 to 0.24 inches).

The thickness of the jian blade is designed to strike a balance between strength, flexibility, and weight. It needs to be thick enough to maintain structural integrity and withstand the forces of impact during combat or training, while also being thin enough to allow for quick and agile movements.

It's important to note that the dimensions of the jian blade can vary based on factors such as the specific design, purpose, and regional variations. Different schools of swordsmanship or historical periods may have their own preferences in terms of blade thickness and profile.

In addition to the blade, the hilt (handle) of the jian also has its own dimensions. The hilt of a jian is typically slender, allowing for a comfortable grip and ease of manipulation.

Overall, the thickness of a jian blade can range from approximately 4 to 6 millimeters (0.16 to 0.24 inches), but the specific dimensions may vary based on the individual sword, swordsmith, and the desired characteristics of the weapon.