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How to Tell If Knives Are Sharp?

The most important tool in the kitchen is a knife. However, no one likes the additional effort to get things done when using a dull knife. Aside from this, using a blunt knife could be very dangerous as it is more susceptible to slipping off. Instead of discovering a dull knife while prepping a meal, what if you learn how to tell if knives are sharp?

There have been many tips and techniques developed over the years. But I will be selecting the best of these techniques and teaching you how to test your knives. 

Identifying a Sharp Knife 

Trying to test your knife for sharpness could be such a scary task, especially when using the finger method. The finger method requires that you run your thumb gently on the edge of the blade. It is quite an intuitive method, and you will intuitively know if the edge is sharp or not.

Three Finger Test of Edge Sharpness by Murray Carter

However, if not well done, it could result in an accident. Thus, you may replace your nail with a plastic pen. If the edge catches the plastic, then it is sharp enough. 

Hence, to avoid this, most people would rather use their knives until they get stuck in the process of cutting because the edges of the blades are no longer sharp. But what if I told you that there are other simple ways of identifying a sharp knife aside from the finger method?

We’ll go over five other techniques to explore how to tell if knives are sharp. 

1. Tomato Test

How to Tell If Knives Are Sharp Through Tomato Test

Tomatoes are soft vegetables with textured skin, and it takes a sharp knife to run through them without any pressure applied. Thus, if you want to know if your knife is sharp, get just one tomato and run your knife through it. If the knife slices through without any difficulty, then it is reasonably sharp. 

2. Arm Hair Test

How to Tell If Knives Are Sharp Through Arm Hair Test

It’s not an uncommon practice to find people scrapping off the hair on their forearm with their newly bought or sharpened knives. But this is one of the best yet insane ways to test the sharpness. A sharp knife will deliver a clean cut when you swerve it across your arm hair. However, if the hair folds over the blade or causes pain while attempting, then your knife needs to be sharpened.  

3. The Paper Test

How to Tell If Knives Are Sharp Through Paper Test

This is perhaps the most common testing method. Hold up a sheet of paper and run your knife through. A sharp knife goes through the entire paper and splits it in half. Suppose it does not cut off the paper or cuts just the edge and stops in the middle, then it means the knife is dull. 

4. Visual Inspection

How to Tell If Knives Are Sharp Through Visual Inspection

This is one of the fastest ways of knowing your knife needs sharpening or honing. The process is simple. Hold your knife against a light source and watch out for a reflection. If the knife shimmers or reflects, then it is dull. A sharp knife comes with an edge with an opaque black line and non-shining teeth.  

5. Onion Test

How to Tell If Knives Are Sharp Through Onion Test

Onions are rebels that require a sharp knife if you seek to conquer them. A blunt or dull knife will slide off the onion when you attempt to cut, or it may require so much pressure from you to slide through. When the effort and pressure you use on the onion are too much, then it’s time to get the knife sharpened.


There are numerous other techniques on how to tell if knives are sharp. However, whichever method you consider, ensure you are gentle with the process to avoid an accident. If your knives are sharp, storing them in the right place and using them with the right food helps retain the sharpness for a long time.

Also, you can attempt using a sharpening steel to hone the edges of your knife if it is not entirely blunt and in need of sharpening. If this is the case, a whetstone, knife sharpener, or tapping professionals to get your knives perfectly in shape can also be explored.  

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