How to Test The Sharpness Of Your Knife

Top 5 Knife Sharpness Tests

If you spend time in the kitchen, you know that a sharp knife is one of the most important tools you can own. But many home cooks don’t realize just how much difference a properly sharpened blade makes. Sharp knives aren’t just easier to use -  they’re safer, more precise, and help preserve the quality of your food.

 

The good news is that you don’t need any special tools to figure it out. With a few simple knife sharpness tests, you can check the edge of your blade right at home and know whether it’s time for a professional sharpening.

 

1. The Thumb Test 

This is one of the oldest and most trusted knife sharpness tests, but it requires a light touch. Gently place your thumb perpendicular to the blade’s edge (never along the length), and slowly draw it across the edge without applying pressure.

• Sharp blade: Feels slightly “tacky,” like it wants to grip your skin.

• Dull blade: Feels smooth and rounded, sliding without resistance.

We usually check near the middle or tip of the blade, as those areas tend to dull first.

👉 Read our guide on knife safety basics.

 

2. The Paper Test

The Paper Test is a popular way to check sharpness, and it’s perfect for showing off how cleanly your blade can slice. Hold a piece of newspaper, printer paper, or a magazine page by one corner. With your knife angled around 45°, slice downward in a smooth, single motion from heel to tip. P.S. Using thinner, more delicate paper is recommended. The thicker the paper, the easier it is for even a dull knife to slice through, which can give a misleading result. Keep that in mind when choosing your test paper.

• Sharp blade: Cuts through the paper effortlessly with no snagging.

• Dull blade: Tears, catches, or refuses to slice through cleanly.

This test mimics the way your knife cuts through soft foods, and it’s often the easiest way to see if a resharpening is overdue.

 

3. The Pen or Nail Test

Take a simple plastic pen (or use your fingernail if you’re confident) and hold it still. Then, place the knife edge against it at a 45° angle and gently draw it across.

• Sharp blade: Bites slightly into the plastic or nail surface.

• Dull blade: Slides across without catching.

We like this test because it simulates how a sharp knife grips and cuts into tougher surfaces like vegetables or meat. It’s also a great option if you’re testing multiple knives quickly.

 

4. The Herb Test

This test is a great way to see how your blade performs with delicate ingredients. Stack a few basil or parsley leaves and roll them tightly. Then, slice through the roll with your knife. Let the sliced herbs rest on your cutting board for a few minutes and you’ll be able to see the results for yourself.

• Sharp blade: Glides through cleanly, leaving neat, bright-green slices.

• Dull blade: Crushes or bruises the leaves, causing discoloration and loss of flavor.

Sharp knives make a noticeable difference in the kitchen, especially for herbs, fruit, and soft vegetables. If you love precision in your cooking, this is one of the most telling tests.

5. The Tomato Test

The tomato test might be the internet’s favorite way to check knife sharpness, but it’s also one of the most misleading. Sure, a knife that glides through a tomato looks impressive, but what you’re really seeing isn’t pure sharpness; it’s how “toothy” or gritty the edge is.

 

When a knife is freshly ground, its edge can have tiny micro-serrations that grab onto the tomato’s skin. That roughness helps it “bite” easily, even if the knife isn’t finely honed. During our sharpening process, we buff out those burrs for a smooth, long-lasting edge. If we skipped that step, every knife would slice a tomato beautifully, but it would dull quickly.

 

This misconception shows up most with Santoku and Nakiri knives, which are designed for clean chopping motions rather than slicing through slippery produce. Their geometry isn’t meant for tomatoes, and forcing them to perform that test can actually give you the wrong idea about their sharpness.

 

For cutting tomatoes (or any fruit with a tough skin and soft inside), nothing beats a small serrated knife. Its teeth are made for that exact job. So, if your chef’s knife struggles a bit on tomatoes, don’t worry — it might just be too refined for that kind of work.

 

When that time comes, don’t settle for just “good enough.” At Sharpen Up 365, we specialize in restoring blades to their original geometry, often sharper than when they were new. Our mail-in service makes it simple no matter where you’re located in the USA: we send you a secure kit, you mail us your knives, and we return them razor-sharp and ready to work.