How to Test a Knife for Sharpness in 7 Quick Ways

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As someone who wasn’t used in the kitchen, it took me a while to realize just how much difference a sharp knife makes. After getting my first whetstone, I no longer let my knives go dull and damaged.

Always making sure to sharpen and hone them lets me have an excellent cutting experience. At the same time, I also came to know the importance of checking how sharp my knives are. That’s why I’m here to share with you the ways on how to test a knife for sharpness.

What You Will Need

What You Will Need

There are a few things you need, which are:

  • Your knife
  • Papers
  • Light source
  • Hair (on your arm)
  • Fingernail
  • Onion
  • Tomato

There are seven sharpness tests in this post, but you only need six materials, excluding the knives. That’s because one of the tests involves you simply feeling if the blade is sharp or not. Don’t worry. It will all be explained in the next part of this article.

How to Test a Knife for Sharpness – Step by Step Instructions

A sharp knife must be able to cut into different things. So, when you want to know how your knife performs, you just need to try it. But if you’re going to go with the standard way of checking knife sharpness, then there are a few tests you can do.

1. Paper Test

How to Test a Knife for Sharpness

The most common and easiest sharpness test, all you need for this is your knife and a piece of paper. To do it, follow this:

  • Slice the paper with your knife
  • If the blade slices the paper easily, then it is sharp
  • The knife should slide through the paper smoothly
  • If it gets stuck or saw through the paper, then it isn’t razor-sharp

You can also raise the level of this test by using a magazine paper or cutting through two layers. If the knife cuts through or at least bite through the layered magazine paper, then it is sharp. A dull blade will never be able to pass through thick paper like this.

Check this video to know how this test is done.

2. Burr Test

Burr Test

One of the simplest methods, the burr test doesn’t only check if your knife is sharp but that it is not over sharpened. If you don’t know, you can ruin your knife if you sharpen it too much. You can prevent that by doing the burr test every few strokers. Here is how:

  • Glide your knife back and forth through the whetstone/sharpener
  • After a few strokes, feel the opposite side of the blade you are sharpening
  • If there is a burr, then you are done sharpening that side
  • Flip the knife and begin sharpening the other side

With the burr test, you get a rough idea when to stop sharpening and ensure you will not accidentally damage the blade. However, the burr test doesn’t always mean that your knife is razor-sharp. In that case, it is a great idea to perform another sharpness test after.

3. Hair Test

Hair Test

This test is a little dangerous, so be careful. If you don’t, you can accidentally hurt yourself. It isn’t the best way to check if your knife is sharp. But if you are unsatisfied with the first two methods, then you can try this. Follow the instructions below:

  • Run the blade through your arm, really lightly
  • Check if the blade shaved off some of your hair
  • If your knife is sharp, it should cut your hair
  • If it is dull, then it will only slide across

4. Light Test

Light Test

In this method, what you simply need to do is check the edge of the knife. A sharp knife should not have any chips and dents. Check that your blade doesn’t have these by bringing it near a light source and inspecting it. You can do that with the following steps:

  • Don’t strain your eyes. Use a light to check the knife
  • Shining a light on a knife, which is steel, will reflect it
  • The reflective light can show the chipped or dented areas

The light test is an easy method, but not very effective. However, it is a quick way to tell if your knives still need sharpening. If you don’t have paper or other tools for checking knife sharpness, this is also a handy method.

5. Fingernail Test

Fingernail Test

This method is yet another dangerous test, just a little less than the hair test. You still need to be extra cautious when performing this way. Shaky hands are a no-go because that is a recipe for disaster. But if you think you can handle it, follow these instructions:

  • Place the blade on your fingernail
  • You won’t feel much if your knife is dull
  • A sharp knife will bite into your nail

This is how the fingernail test is done. Using your nail, you can feel if the blade’s edge is sharp. However, be sure not to add pressure when performing this method. Even the slightest pressure could end up with the knife cutting into your nail and fingers.

6. Tomato Test

Tomato Test

If you have a tomato, then you can use it. It is hard to cut a tomato with a dull knife. If your blade is dull, it will flatten the tomato because it is soft and slippery. It’s a safe method and thus recommended. Try it like this:

  • Take out your knife and a tomato
  • Bring down the blade onto the tomato
  • See if it cuts the tomato easily
  • If it slides or flattens the tomato, it is dull
  • If it cuts through easily, then it is sharp

7. Onion Test

Onion Test

The onion test is a lot like the tomato test. Both are an excellent method of testing knife sharpness. That’s because you are actually cutting the things you are supposed to cut. Onion is soft with a slippery peel, which makes it hard to cut through with a dull knife.

  • Rest the edge of the blade on the onion
  • Without too much pressure, cut through it
  • The knife won’t bite if it’s dull
  • It will go through if it is sharp


There it is – these are how to test a knife for sharpness. Did you enjoy this how-to? I’m hoping you do and that you learn something of value. If you are always in the kitchen, I cannot emphasize more about how important a sharp knife is for easy work. In addition to learning how to sharpen and hone your blades, knowing how to test it is also useful info.

Knife sharpening tips:

Quick Tips on How to Sharpen Henckel Knives Like a ProHow to Sharpen a Convex Edge

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