The Rockwell hardness scale is a standardized scale used to measure the hardness of materials. It's often used to determine the hardness of steel, including the steel used in kitchen knives.
The Rockwell scale measures the depth of an indentation made by a small, hard ball under a specific amount of force. The resulting measurement is expressed as a Rockwell number, which is a unitless number. The higher the Rockwell number, the harder the material.
In the case of kitchen knives, a higher Rockwell number indicates a harder blade that will hold its edge longer. However, a harder blade may also be more brittle and prone to chipping or breaking. On the other hand, a softer blade may be more flexible and resistant to chipping, but it will need to be sharpened more frequently.
When it comes to kitchen knives, Rockwell hardness ratings typically range from 52 to 66. Knives with a Rockwell hardness of 52-56 are considered soft and are good to cut through harder materials such as bones. Knives with a Rockwell hardness of 57-62 are considered medium hard and are good for a wider range of tasks. Knives with a Rockwell hardness of 63-66 are considered hard and are good for tasks that require a very sharp edge, such as filleting fish or slicing raw meats.
In general, the Rockwell hardness of a kitchen knife is just one factor to consider when choosing a blade. Other important factors include the type of steel used, the blade's edge geometry, and the handle material. By considering all of these factors, you can find a kitchen knife that's well-suited to your needs and preferences.
For a detailed guide with everything you need to know about (Japanese) kitchen knives read our ultimate kitchen knife guide here.