How to Test Knife Sharpness

Fact Checked By:Aithley Balder

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A knife’s sharpness directly correlates to how well it performs its intended function. However, it might be difficult to tell whether a person’s knife is sharp or dull. The standard definition of a sharp knife or blade is one that can easily penetrate any material, regardless of the force applied to it. However, this is only partially correct, since a sharp knife can effortlessly slice through any thickness with no effort, whereas using a dull one wastes time and effort.

In light of this, it is essential that you test the sharpness of your knife before using it. Your time is therefore conserved. If your knife isn’t sharp, how can you use it effectively? Checking and maintaining a knife’s sharpness is the subject of this article.

How often is it recommended that knives be sharpened?

Depending on how often you use your knives, you should only need to sharpen them every few months; nevertheless, I would suggest getting your knives professionally sharpened every one to two years.


To determine definitively whether your knife is sharp, you should test its capacity to cut through a range of items. However, you will need to begin working with the knife before you can determine this, which may cause harm to whatever you are working on. Because of this, you should always make sure a knife is sufficiently sharp before using it for serious work. The following are a few methods you may use to evaluate the sharpness of your knife.

how to test sharpness of knife

The Onion and Tomato Test

You read and understood it correctly. Onions and tomatoes, two of your go-to kitchen staples, may serve as a handy gauge of knife sharpness. If a knife can easily pierce an onion’s peel, it has been deemed sharp enough to pass the onion test. But if the knife is dull, slicing through the onion’s peel becomes a formidable struggle.

Tomatoes, however, have naturally tender flesh that makes them simple to dice. However, it possesses a strong exterior flesh that is difficult to break. Put the blade on top of the tomato without exerting any pressure and draw back to see whether it cuts cleanly (retract your hand, without applying a downward force). If the knife can slice the tomato into two even with this motion, then it is a sharp knife worthy of attention. Cutting a tomato into uniform bits for cooking might be difficult if you have a dull knife since it takes more energy to cut through the peel.

Shaving Test

This test is the next we will be considering. It is risky and thus needs to be done cautiously, ensuring you don’t damage yourself in the process. Cutting the hair from beneath your arms with your knife. When you run a knife down the hairs on your arm, a sharp knife will cut them out, while a dull knife will have no effect. Keep your hands away from your underarms; doing so might result in a cut if your knife is sharp. Don’t forget your underarm is the last area you would want to get an injury since it is unpleasant.

The Paper Test

The phrase “oldest trick in the book” is often used to describe this method. Good news is that you may use whatever scrap of paper you find. If you want to take this quiz, you don’t have to buy any particular paper. To achieve this, take any piece of paper, hold it in place with your fingers so that you can slip your knife into the top area, and then draw the knife outward. A well-honed knife can easily split the paper in half lengthwise. However, a dull knife will leave jagged edges on both the cutting board and the slips. Even worse, it may rip or come loose.

Another way is to use a glossy magazine or a printed phone book. Due to the complex nature of these papers, this procedure verifies the sharpness of your knife. This makes it difficult to catch the paper with the blade of a knife. Because of this, a dull knife would impede the process. However, a sharp knife that has been folded or wrapped up may easily accomplish the task at hand. Surprisingly, toilet paper requires even more work to cut precisely with a knife. To that end, test your knife on some cardboard; if it slices through, you know just how sharp to make it.

The Fingernail Test

If you’re like me and don’t perform well under pressure, this exam is calling your name. It comes in helpful when you’re already sat and about to begin your knife activities, and then you suddenly recognize the necessity to inspect how sharp is the knife. You don’t want to leave that location to go get any of the aforementioned things, so you use your fingernail.

For this, you may use either your thumb or index finger. Holding the knife so that its edge is resting lightly on top of your fingernail, you can get it to rest perpendicular to your finger. When a knife can cut through a fingernail without any assistance from you, you know it’s razor sharp. But if it slips off the fingernail, it’s dull and has to be sharpened again.

Visual Test

This task demands good vision so that you can identify the knife’s edge and determine whether or not it is sharp. Human eyes may be helped in two ways: either by using a light source or a magnifying lens. If there is any reflection while holding the knife up to a light, you know it’s a dull one. A sharp knife, on the other hand, will produce a straight and consistent black line.

Using a magnifying lens, check the edge of the blade to see whether it is sharp; a straight black line indicates a sharp edge. Scanning electron microscopes are the best instrument for the job. However, they may be rather expensive to acquire, so if that’s a problem, you can always use a loupe in conjunction with the light.


How should you determine whether or not your tools are sharp?

Try cutting off a portion of the end grain and seeing how it tastes. If the cutting edge of the tool is dull, it will only be able to press the grain down and will not be able to cut off shavings. When the cutting edge of the tool is sharp, it will cut the end grain neatly, resulting in shavings or ribbons, as seen in the following image.

How do you determine whether or not a chef’s knife is sharp enough to use?

The good old-fashioned paper exam is perhaps the one that has been used the most successfully throughout the years. Take a piece of paper, place it in the space created by your fingers, and then move the knife in a downward direction. The weight of the knife alone, assuming the blade is sharp, will be sufficient to neatly and quickly shave through the paper. When something is dull, it will often become ragged or fall off completely.

How can I test the sharpness of my knife?

The sharpness of a knife may be evaluated by testing it on your fingernail, which is the method that Work Sharp uses when demonstrating its products at knife exhibits and sharpening events. The procedure is simple. Tap the edge of the blade on your fingernail in a soft and gentle manner. If the blade of your knife bites into whatever it is cutting, then it is sharp; if it deflects or slips, then it is dull.

Some other diagnostic tools

A good knife may be judged by its ability to whittle hair without causing undue strain on the user.

You may use your tongue as a test for the sharpness of your knife; I wouldn’t recommend it, but hey, if you’re feeling brave, go for it. Eventually, I pray you get to savor your meal.


If you want to get things done quickly and simply, a good knife or knife set is essential. It might be difficult to labor in the kitchen, grocery store, or workshop when this is not immediately acknowledged. Is it your desire to learn how to check the sharpness of a knife? If that’s the case, you’ll find some helpful information below. We have gone through the five most reliable techniques to check the sharpness of your knives, plus two more options. Both of these ways are worth considering the next time you need to double-check that your knife is razor-sharp.

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Aithley Balder

Hello there, my name is Aithley Balder from Texas. I am a cookware, sewing, toilet, technology enthusiast and I have been sharing my passion with my friends and likeminded folks for close to 4 years now. Don’t hesitate to get in touch with me via the contact page.

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