11 Blade Sharpness Testing Techniques To Check Knife’s Cutting Edge

How sharp is a razor blade? Do you want to know how to test blade sharpness?

Kitchen knives are very useful, but most do not care enough to check if it is still sharp until it needs a knife sharpening service. You have to learn how to care and maintain your kitchen knives  You should anticipate that your kitchen knife won’t stay razor-sharp forever. Its razor blade will eventually turn dull after months or years of use.

Unfortunately, most are not well oriented when it comes to blade sharpness. Most people don’t even know how often to sharpen their knives to keep its cutting edge.

Do you want to know how sharp your knife is? Want to make sure if its sharpness is still enough for safety usage?

If you want to know whether your knife is still sharp, I’m glad to tell you that there are a lot of ways to determine that. I’ll be sharing various types of razor blade sharpness testing to let you know whether your knives already need a sharpening service or have good edge retention.


1. Paper Test

Source: knifeblog.com

Paper is one of the most common materials when testing the sharpness of a knife. At the same time, it is probably among the easiest and most convenient strategies that you can try on.

You simply need a paper to pull this. If you are ready with your paper and knife follow the instruction below

How to do Paper Test

1. Get a standard sheet of paper. A copy paper is the best.
2. Hold the sheet of paper firmly at the top with one hand.
3. Draw the blade down through the paper heel to hip using the other hand.

How to examine the result: If the knife glides through the paper with minimal pushing, then your knife is still sharp.

Otherwise, if it snags, then you need to realign the edge of the blade by honing using steel or sharpen using sharpening tools like water stones. Then, repeat the paper test.

2. Hair whittling test

This strategy is best for advanced knives. It’s not an easy task, but if your knife makes it then it only means that you have the sharpest knife in hand.

How to do it

1. Get a strand of hair. Longer hair is recommended because short hair is very difficult to cut.
2. Run the hair through the knife’s cutting edge.

How to examine the result: If the knife successfully whittles the hair then it has a sharp razor blade with the sharpest edge and superior edge retention. Otherwise, it fails the test. But remember, this test is one of the toughest ones when it comes to testing your knife’s sharpness.

3. Three-finger test

Master bladesmith Murray Carter recognized this sharp knife test. However, it is only suggested for skilled smiths because it is not easy to do. The test demands carefulness, knowledge, and tons of practice because the tester has to run his fingers along the sharp edge of the blade. Three fingers are used, that’s why the test is called the “three-finger test.”

How to do it
1. Put the thumbnail on the opposite side of the sharpened edge of the knife.
2. Put the next three fingers on the sharpened edge or razor blade. Only apply very light pressure on the blade edge carefully.
3. Feel the sharpness of the cutting edge. Be very careful that you do not back and forth the knife.

How to examine the result: If the knife is dull, you will feel it because it allows you to have constant back and forth. However, a sharp knife catches the back and forth of the fingers and will make it stop.

4. Tomato test

Source: boingboing.net

Most of us have tomatoes in the kitchen, so if you want an easy alternative for the paper test, then this is it. Tomato is a good material to test your knife’s sharpness because it has tough skin but is very soft inside.

You will easily realize whether you have a sharp knife or not depending on the result after you slice the fruit.

How to do it

1. Grab a tomato. The riper the tomato the better because it would be harder for the knife to slice it.
2. Place the tomato on a cutting board and start slicing without putting any effort.

How to examine the result: If the knife is sharp it will cut through the tomato smoothly. You just have to hold the knife Otherwise, it will end up smashing the fruit.

5. Fingernail Test

Our fingernails are covered with alpha-keratin which serves as its protective layer. It is hard enough to do the test which makes it a nice trick for measuring the sharpness of a knife-edge

How to do it

1. Put the sharp edge of the knife on the fingernail. Thumbnails work great for this test.
2. Shave the nail. Make sure not to put too much pressure on the thumbnail.

How to examine the result: A knife with a sharp blade will catch the nail and won’t move. However, if the blade is dull it will slide around without catching the nail.

6. Tongue Test

Some edge sharpness tests are strange while others are hilarious. This type of sharpness testing belongs to both because it is strange and hilarious at the same time.

Many do not recommend it, but you can see a lot of videos of people doing it. Others might not find it comfortable to test the sharpness of the knife’s edge.

If you are willing to take the risk, it is important to note that it requires a certain ability to pull off the technique.

How to do it

1. Place the knife’s cutting edge on the tip of your tongue.
2. Feel the edge of the knife with your tongue You can slide either the tongue or the blade back and forth to get a good feel of the cutting edge’s quality and sharpness.

How to examine the result: You will know when the cutting edge is sharp by simply feeling it. Do you feel any burr, if not then your knife is good. Experts can easily identify the edge sharpness if it is okay or not. However, this test might be tricky for some who has no idea how to test knives using their tongue.

7. Onion Test

Source: brightonyourhealth.com

This is similar to the tomato test but instead of using a tomato, you will use an onion.

The skin of the onion is very thin and slippery which makes it a great material to test your knife.

How to do it
1. Get an onion and put it on the chopping board
2. Start slicing the onions using the knife.

How to examine the result: If the knife cuts through the onion smoothly then your knife is still sharp.

Otherwise, it will keep sliding on which means that you need to sharpen the blade of your knife.

8. Visual inspection

This is probably the most convenient knife test that you can try on because you do not need any other material than your knife. It sounded easy but it can be tricky. It requires a set of skills to know

How to do it
1. Look directly at the blade edge with a light source behind you.
2. Examine if you will see any reflections. You can use a magnifying glass to make it easier. But even a sharp edge will look rocky when enlarged.

How to examine the result: If you see reflections that suggest that you are looking at the dull, bent, or chipped areas of the knife. If you see an almost invisibly smooth black line cutting edge, then your knife is still sharp.

9. Shaving arm hair test

Another easy and convenient way to test your knife’s sharpness is by shaving your arm hair. It is convenient because you do not need any tools other than your knife. However, it is recommended that you be cautious when doing this.

How to do it

1. Ready your knife and your arm.
2. Shave the hair on your arm using the knife.
3. Observe if the knife will successfully shave the hair in your arm.

How to examine the result: If the knife easily shaves the hair, then it is still sharp. Otherwise, if it doesn’t deliver what you expect from it, then it is dull.

10. Blade Wand Test

Source: beaverbushcraft.co.uk

One of the preferred ways to test a knife’s sharpness is by using a blade wand, a piece of animal horn or hard plastic that allows you to test your blade for sharpness and micro nicks and chips that may be present on the blade but too small to notice in the naked eye.

Compared to other knife tests, this is very safe and controllable that even children and those prone to accidents can use this blade test with confidence that they won’t get themselves injured.

How to do it

1. Hold the blade downwards at an angle of about 60 to 70 degrees to the horizontal.

2. Rest the cutting edge gently on the long side of the wand under its own weight

How to examine the result: If the blade slides down the length of the wand then it is dull and needs sharpening. But if it remains where it is placed and does not slide down the length then it is still sharp.

11. Thumb Test

Another easy way to test knives without any testing tools or products is the thumb test. This sounds like the three-finger test, but in this technique, you will only be using your thumb to scrape the knife.

How to do it

1. Clean your thumb.
2. Take the edge and let your thumb go limp.
3. Grab it in the same bite as the micro serrations that happen when you do the shaving arm test.
4. Move your thumb back and forth.

How to examine the result: If you do not feel any burr on the edge, then your knife is razor-sharp. Otherwise, you have to sharpen the edge or fix the edge bevel.

Wrap Up

There are many techniques to check if the razors or blades are razor-sharp. Many of them do not need any tool to be done. So, if you aren’t sure whether you need to hone or sharpen your knives, then you should try the recommended knife sharpening tests above.

Some tests require certain skills or abilities to pull off. Others need extra caution because it can end with you injuring yourself. If your knife fails the sharpness test, then go on and sharpen or hone it. You can use sharpening tools and products to sharpen the blades or cutting edge.

Also, while you can sharpen your knife on your own, it is highly recommended that you have your knives professionally sharpened after 1 or 2 years. They’re knowledgeable in aspects like best knife steel material and many more.

If you wish to learn more about sharpening knives, finding the right chef knife and more,  please check our homepage.


  • cooksillustrated.com/how_tos/9398-testing-knife-sharpness
  • worksharptools.com/how-do-i-know-if-my-knife-is-sharp-or-dull/
  • jeffpeachey.com/2016/10/04/twelve-ways-of-testing-knife-sharpness/
  • lansky.com/blog/5-ways-test-how-sharp-your-knife/
  • japaneseknifereviews.com/01/2021/how-to-test-knifes-edge-sharpness-6-different-process/

Image Sources:

  • shopify.com
  • knifeblog.com
  • boingboing.net
  • brightonyourhealth.com
  • beaverbushcraft.co.uk