How To Tell If a Knife Is Sharp: 7 Ways to Test Your Knife’s Sharpness

There’s nothing worse than a dull blade. I’ve said this countless times, but I can’t stress it enough. Never use your knives when they are dull!

This is not only difficult to use but also very dangerous. When your blades are not razor-sharp, there’s a big chance you’ll cut yourself. So though sharp knives may seem dangerous, they are actually safer than dull ones.

But how do you know when your knife is sharp? How do you avoid oversharpening your blade?

Today, we’re going to have a look at 7 easy ways to test the sharpness of your knife. With these, you’ll know right away whether your knife is sharp or dull.

The Paper Test

One test I talk about a lot in my previous articles is the paper test. For me, this is the easiest and best way to test the sharpness of your knife. All you will need for this test is your knife and a piece of paper.

To do this test, try slicing the paper with your knife. If the knife catches the paper and slices it easily, you have a sharp blade. It should slide smoothly through the paper. If it gets stuck, or if you have to saw it through, your blade isn’t razor-sharp.

The paper test is a very satisfying one. There’s something about the knife gliding through the paper that makes you feel so good. Give it a try yourself. If you’re like me, you’ll love it.

If you want to take this test to the next level, use magazine paper. Magazine paper is very thin and glossy. Only the sharpest knives can cut through this with one stroke. The rest are going to slide right off.

For the ultimate test, fold your magazine paper, and try cutting through two layers of it at once. This is the final method. Only the sharpest of the sharp will bite through folded magazine paper. If there is dullness in your blade, it will never be able to do this.

The great thing about this test is how easy it is. Just grab a piece of paper and slice at it. When I sharpen my knives, this is the test I like to use.

The Burr Test

Oversharpening is a real problem. When I was new with knives, I ruined some of my blades because of this. I thought that there was no limit to sharpness. I thought that if I kept on sharpening, my knives would keep on getting sharper.

This is not true. If you sharpen more than necessary, you’ll damage your knife instead. This is why every few strokes, it is a good idea to perform the burr test. I use this all the time, regardless of what sharpener I’m using.

To perform the burr test, all you have to do is feel your blade after every few strokes. You want to feel opposite the side you are sharpening. If you feel a burr, rough material, this means you are done sharpening. Flip your knife and you can work on the other side.

The burr test gives you a good idea when you should stop sharpening. This ensures that you don’t damage your blade. However, there will be some times when your knife won’t be razor-sharp yet with the burr test. That’s why I like to use this with the paper test as well.

The Light Test

One way to tell if your knife is sharp is by looking at its edge. The last things you want to see are dents and chips here. If they are present, your knife isn’t going to cut well at all.

This is why a visual inspection of the edge is a great idea. If you see any chips or dents, your knife needs sharpening. However, this is a lot harder to see than you might expect. It only takes tiny imperfections to render your knife dull.

That is why instead of straining your eyes, you should use light. Steel is reflective, when you shine a light on it, it will shine right back. This way, it is very easy for you to see these tiny dents and chips.

If your blade is perfect, the light will form a straight reflection on the edge. If there are some areas where the light cuts, these are the areas that are dented or chipped.

This isn’t the most effective way of telling if your knife is sharp. But if you’re looking for a quick way to tell if you need to sharpen, use this method. This is also great if you don’t have anything with you.

The Hair Test

Another test I use a lot is the hair test. Whenever you perform this test, you need to be very cautious. If things go wrong, you could hurt yourself. That’s why this isn’t the best way to test your knife’s sharpness.

The reason why I use this is because there are times when I don’t have anything around. I could perform the light test. But again, the light test will only tell you if there are imperfections, not if your knife is razor-sharp.

So what is the hair test? The hair test is when you test your blade on the hair of your arm. Run the blade lightly through your arm and see if it shaves off the hair. Only sharp knives can cut your hair this way. If there is any dullness, it will slide across your air without catching anything.

It goes without saying that you need to be very careful when you do this. One slip and you will cut yourself. That’s why I only do this whenever I don’t have anything around. The paper test is a much safer way to do things.

Also, there is another way to performer the hair test which is described in the below video.

The Fingernail Test

If you feel that running your knife through your arm is too dangerous, go for the fingernail test. Again, this is a test that requires a lot of caution. If you have shaky hands, you may want to do something else.

Sharp knives have a lot of bite. This is why they can slice through smooth surfaces such as paper. This is what the fingernail test is trying to find, that bite.

Place your knife on your fingernail. If the knife is dull, you won’t feel much. If the knife is sharp though, you will feel it biting into your fingernail.

That’s the fingernail test. Feel the edge of your blade on your fingernails. Do not add pressure. It is another dangerous test that I do not recommend for all people.

The Onion Test

If you don’t have paper around and don’t want to risk cutting yourself, go for the onion test. This is a great test. The reason I say this is because it is an actual test. We use our knives for cutting things like onions, so why not test it on onions?

Why an onion? Onions are soft, and dull blades can cut through them. So why this test? The answer is in the peel. Onions may be soft, but they have a very slippery peel. It is this slippery peel that will prove your knife sharp or dull.

Rest the blade of your knife on the onion. Don’t put too much pressure, otherwise, the test won’t work. Like every other test, if your knife is dull, it won’t bite the onion peel. If your knife is sharp though, it should go right through the skin.

The Tomato Test

Don’t have an onion? Use a tomato! Most of us have tomatoes in our kitchens, so why not test your knives on them?

Unlike onions, tomatoes don’t have slippery peels. What tomatoes have is a very soft interior. It’s very easy to squeeze a tomato and flatten it.

This is why if you try to slice a tomato with a dull knife, it will flatten the tomato. But if you use a razor-sharp blade, it will create clean slices. Even if you don’t press the knife against the tomato, your knife should cut it.

Your tomato should be in perfect shape after this test. If you have to force the knife through the tomato, it needs sharpening.


With these tests, you should know when your knives are good to go. Again, never use a dull knife. It only takes a few strokes to sharpen, but it takes days, weeks, or even months to heal a wound. Also, you’ll have a much harder time cutting.

That’s why you should always test your knife. Before every use, test your knife. With these 7 tests, you’ll always know if your knife is razor-sharp. You never have to guess if you need to sharpen or not anymore. And the risk of oversharpening will be a thing of the past.

So use these tests. They will make your life so much easier.


I’m Ahmed, the guy behind I’ve owned several types of knives and sharpeners over the last few years and have become obsessed with everything to do with knives. I’m always trying to improve my cleaning and sharpening process, and always on the hunt for the next best knife. But when I’m not spending time with my hobby, I’m here, writing about Knives and Sharpeners on KnifePulse to share with you what I learn along the way.

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