How Sharp is a Katana: Separating Myth From Reality

The katana is the samurai Japanese sword often known as the sharpest blade in history that easily slices through anything. While many tales highly exaggerate its capabilities, the katana blade is still extremely sharp when handled with proper technique and should not be underestimated.

In this article, we will delve into the world of katana sharpness. We will separate the myths from the facts and explain how sharp the katana truly is. We will start by explaining the difference between sharp and blunt katanas and determine what their sharpness can achieve and cannot. Then, we will review what can make a katana sharper than other blades and how to test it.

Sharp Katana Vs. Blunt Katana

A sharpened and ready-for-cutting practice katana is called a shinto, translating to real sword or live blade in Japanese. These katana swords are sharpened throughout the blade from the hilt to the tip by various methods. The art of Japanese polishing started in the Kamakura period (1185-1333) by expert polishers called togishi, who, today, are still actively working on authentic nihonto blades.

The shinken katana is a popular sword today, mostly used for cutting practice against various targets such as bamboo or a tatami mat. Shinken katana blades were also a beloved edged weapon used by samurai in battle or everyday life as a last resort. Today, Japanese sharp shinken katanas are used in the Battojutsu blade art and for cutting practice.

The blunted version of a katana sword is called an Iaito or sometimes mogito or mozoto, translating to practice sword, imitation sword, or in some cases, fake sword. It is an unsharpened version of an authentic katana sword traditionally made of aluminum zinc alloy in Japan. Outside Japan, the laito can sometimes be made from carbon or stainless steel. It is used in Iaido, a Japanese blade art consisting of katana strikes, stances, unsheathing or sheathing the sword, larping, cosplay, and decor.

Katana Sharpness – What Can a Katana Cut Through?

The katana, while often found in legend with tales of its unmatched sharpness, from slicing stones and metals easily, would not live up to these exaggerated feats as it has been tested and scientifically proven multiple times. Nonetheless, its edge and sharpness should not be underestimated and are still a real accomplishment in the sword world.

It can be sharpened to a great extent to cut through several targets with ease and sometimes with a single slash. It can also hold an edge significantly well if it is not made to be as sharp as a razor’s edge and isn’t used on hard surfaces. Here are a few targets a katana can or cannot cut through.

• Humans – backed up by the samurai tales, the katana could slice a human in half, as seen in various tameshigiri tests with a maximum count of 7 bodies at once when placed in certain positions
• Bamboo – a stiff bamboo stick having the same properties as human bones can be cut with a katana
• Tatami mats – the most popular modern tameshigiri target made of wet rice straw, which a katana could slice through and chop off with ease
• Plastic bottles and cans – water-filled bottles or cans are some of the most used backyard katana-cutting targets that the katana can slice through without difficulty
• Wooden logs – depending on the type of steel in use, a katana would be able to cut through wooden logs
• Armor – the katana blade is not ideal for cutting through heavy armor because the blade is primarily made to focus on proper cutting techniques rather than brute force
• Metal – a katana may be able to cut through certain thin layers of metal, but it would damage the blade and its edge beyond repair
• Stone – it is possible to crack smaller stones with a katana blade, but the sword will likely break or crack 

Sharpness alone is not the most important factor when cutting through different targets. A samurai in battle would not bring a razor-edge sharp katana as it would likely destroy the weapon’s integrity. During the peaceful Edo Period (1603-1868), however, the katana was mostly used for cutting practice targets, so it fashioned a much sharper edge than battlefield katanas.

Levels of Katana Sharpness

The sharpness of a traditional katana could be classified into several levels depending on how well it did after a tameshigiri test. The test was done on criminals, slaves, or deceased bodies stacked on a dodan. The dodan was a slope of earth placed sideways where the bodies had their hands and legs tied up and widened.

• Saijo o-wazamono – exceptional cutting sword 
• O-wazamono – excellent cutting sword 
• Ryo-wazamono – very good cutting sword 
• Wazamono – good cutting sword 

Specific cuts were made based on various difficulties. If a katana were more effective at a certain angle and specific cut, it would be ranked higher or lower on a sharpness scale. If the katana’s sharpness and quality were tested on a live body, it was called iki–dameshi. If its quality was tested on a dead body, it was referred to as a sinin–dameshi; if it was tested on hard surfaces such as iron, it was called katamono–dameshi.

The rating is based on a book by Yamada Asaemon, the main executioner and examiner of blade qualities under the Tokugawa Dynasty in 1797. This four-level scale focused on the quality and performance of a shinto blade, where sharpness was one of the most important factors. 

What Makes the Katana Sharper?

The katana is a sword made of steel, like many swords worldwide. All steel can be sharpened to a razor’s edge for cutting, enabling a smaller double-edged arming sword to have the same sharpness as a katana. 

A katana shines in the sharpness factor because its single-edged blade with a stronger taper and bevel, accompanied by a larger handle and a shorter blade, can make it easier to perform a greater edge alignment on its target when compared to other swords.

There remain many different types of katana throughout history and today. Some katana swords can be sharper and retain their sharpness better than others, depending on these important factors.

Steel Type

Depending on the type of steel used to forge the katana, its sharpness and retainability will differ greatly. An authentic Japanese nihonto katana is made out of tamahagane steel, a high-carbon blade that is functional and effective for cutting tests. It can be sharpened to a great extent and perform tremendously, but its edge retention and sharpness fall short compared to modern steels.

Modern 1060 or 1095 carbon steel is great for achieving high levels of sharpness and retaining an edge. Blades that achieve the highest wear resistance and sharpest edge retention are katanas made of 5160 spring steel and L6 tool steel. More important than the type of steel, is the bladesmith working with the steel and the heat treatment process.

Hardness

The hardness is the level of rigidity and strength that the spine and edge of the blade will have, which allows for higher sharpening levels. The traditional hardening of a katana is done through clay tempering.

The ideal level of hardness of the edge for a katana sword is around 58-62 HRC (Rockwell scale C), a method and measurement of the hardness of a blade. This will perform exceedingly well in cutting practice tests without becoming easily damaged. The hardness of an edge can be higher, raising its sharpness level. Some believe the Muramasa Katana, made by the legendary swordsmith Muramasa, reached an HRC 72.

This is highly disputed because a carbon steel blade with more than 65 HRC would need chromium, tungsten, vanadium, or molybdenum, while Japanese tamahagane was never alloyed. Although it is possible to reach an outstanding level of katana sharpness with higher hardness levels today, it will tamper with the blade’s integrity and longevity.

Blade Shape and Edge

The sharpness of a katana can differ and have unique levels of sharpness depending on the type of zukuri blade shape. Some zukuri blade shapes excel in certain sharpness tests, while others give it a more rigid and safe structure to satisfy battle needs.

There are many different types of zukuri on a katana sword. Some of the most popular are the shinogi–zukuri, hira–zukuri, and shobu–zukuri. They differ in blade shape, curve, width, and thickness, and the bevel aims toward the edge. The more bevel and taper a katana edge has, the more polishing can result in a sharper blade.

Most katanas, however, do not feature strongly tapered blades because increasing the level of sharpness automatically decreases the niku part of the blade, which is the thickness of the spine, giving the sword its backbone and making it more resilient to breaking.

Sharpening

A katana’s sharpness level is largely influenced by the sharpening done on its edge. This can be done in various ways, such as traditional polishing on a whetstone or using a sanding belt to run across its edge and bevel. The traditional Japanese sharpener of the katana is called a togishi, whose training takes twice as long as the smith making the sword, meaning that the sharpening is one of the most important things to get right.

The sharpening done on a katana is limited by how much the user wants it to be sharpened. This can be done over a lengthy period, which can make it razor-sharp, or until the blade satisfies some of the techniques used to test the ideal sharpness of a katana blade.

How to Test the Sharpness of a Katana?

The katana is sharpened to the satisfaction of the bladesmith so it can functionally cut through its intended targets. In history, the main target of the katana was human soldiers, so its traditional sharpness test was practiced on humans. This is called tameshigiri, and the bodies of criminals and slaves were stacked on each other to test the katana’s sharpness.

Today, the sharpness of a katana is tested in a less gruesome manner. Some preferred options are a paper-cut test, shaving test on body hair, modern tameshigri practice on tatami mats, or going through a BESS tester.