What is the Rockwell Hardness Scale?

If you have spent any time at all in the kitchen, you’ve probably noticed that all kitchen knives are not created equally. Since there are many types of steel and processes of knife-making, there must be a knife material rating system so that professional chefs and home cooks can easily compare types of kitchen knives.

The Rockwell Hardness Scale is the system used to determine the precise strength and sharpness of steel for knives. When looking for the best blade, this scale can tell you everything from which kitchen knife is made from harder steel to which offers a sharper cutting edge.

What Is Rockwell Hardness?

Created by Stanley P. Rockwell in 1914 as a new way to measure the steel ball bearings manufactured at his company, the Rockwell hardness test was eventually found to apply to any type of metal as well as non-metallic materials.

Today, the Rockwell Hardness Scale is the standard method to measure and determine the strength and quality of a kitchen knife blade.

How Is it Measured?

The Rockwell Scale is used to determine the hardness of a metal by measuring the depth of the indentation made after a conical diamond impacts a piece of metal. Since diamond is the hardest natural substance on the planet, it is the perfect choice to use for the test impact.

The test is performed twice. During the first test, a minor amount of pressure is applied to the metal and the indention is measured. During the second test (in the exact same position), the pressure is then increased to about 300 pounds and the diamond-shaped indentation is measured again.

The difference between the first indentation depth and the second indentation equals the hardness of the knife blade. Since the hardness of steel does vary greatly, many manufacturers offer a hardness rating range for their steel knife products for easy recognition of its qualities.

What Do Rockwell Score Ratings Mean?

There are actually 30 different Rockwell scales that are used to determine the hardness of a kitchen knife. They all use a unique combination of testing variables including different forces as well as different types of indentation.

Once a knife is made, it is given a Rockwell Score rating because this score is known to be standardized, fast, and reliable.  The Rockwell scale uses letters of the alphabet for ratings.

The most important Rockwell scale for measuring the steel of knives is the Rockwell C Scale, often shown as an HRC score. When using an HRC score, the steel’s resistance to permanent distortion is being measured.

A great example for hardness standards on the Rockwell scale is to assess the HRC score of a typical ax with a sharpened edge, which is around 50 HRC when it can cut through a piece of wood without any issues. Here are the HRC scores for kitchen knives:

• An HRC score below 52 means that the knife blade is way too soft to be used as a kitchen knife.

• Stainless steel that has an HRC rating between 52-54 is considered to be somewhat soft, but could be used to make an inexpensive kitchen knife.

The best rating for kitchen knives is an HRC score between 59 and 64. Any score above this would make the knife blade extremely brittle, which means that the blade could actually break while using it.

Professional chefs as well as experienced home cooks will want to choose a kitchen knife that has an HRC rating of 55 and higher for best results when cooking. For reference, all Made In Knives have an HRC score of 58+.

• Kitchen knives made with softer stainless steel are more durable.

• Knives with ratings in the low 50s will not hold its sharp edge as well as those with higher RC ratings.

• Knife blades with low RC scores are easier to hone or sharpen and require less maintenance skills.

• A kitchen knife with an HRC in the 50s offers higher tensile strength, or the resistance a material exhibits to breaking under tension.

• A kitchen knife made from harder steel is able to better maintain its sharp edge.

• If the steel blade is too hard, it will become brittle and more likely to break during use.

• Knives with RC scores over 65 tend to be more susceptible to damage.

• Blades made with harder steel will take longer and more effort to sharpen.

Ready to Shop?

Because every Made In Knife has an HRC of 58+, you know you’ll be getting a strong and durable Knife that’s still easy to sharpen and maintain. Through knowing more about the Rockwell Hardness Scale, you’re now able to confidently shop for a kitchen knife that makes mincing, slicing, dicing, and prepping ingredients a breeze.