The allowable length of a fixed blade knife can vary depending on the jurisdiction and its local laws. In the United States, for example, federal law does not specify a maximum length for fixed blade knives, but individual states and cities may have their own regulations. Some states impose restrictions on the length of fixed blade knives carried in public places, while others do not have specific length limitations.
In general, common fixed blade knives used for everyday tasks and outdoor activities typically have blade lengths ranging from around 3 to 7 inches (7.6 to 17.8 cm). These sizes strike a balance between usability and portability.
If you're considering purchasing a fixed blade knife, it's essential to research the local laws and regulations in your area to ensure compliance with the specific length limitations, if any. Always exercise caution and follow local guidelines when carrying or using any type of knife.