Sharpen Up

5 Ways to Tell If Your Knife Needs Sharpening

updated May 1, 2019
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(Image credit: Christine Han)

Cutting with dull knives not only makes prep worker harder, but it’s also dangerous. Unfortunately, there’s no set interval to tell us how often to sharpen these trusty tools, but there are a few telltale signs that will keep you clued in. Not quite sure if it’s time to sharpen your knife? Put it to one of these five tests to find out.

1. The blade feels dull.

It’s useful to get familiar with the way the blade of the knife feels, albeit very carefully. Gently run your fingertips over the edge of the blade. Sharp knives simply feel sharp, with a blade that has a well-defined, distinct edge. On the other hand, if the blade feels dull or rounded, you’re knife will benefit from being sharpened.

(Image credit: Pam Krauss)

2. It’s not sharp enough to cut paper.

A piece of paper (standard white paper or even a magazine page will do) is a fast and easy way to tell if your knife needs sharpening. Hold the paper upright, and with your other hand hold the knife at the top edge and slice downward. A sharp knife will slice the paper cleanly in two. It’s time to sharpen your knife if the blade slides off the edge or rips the paper unevenly.

(Image credit: Christine Han)

3. It smashes tomatoes.

How well does your knife slice tomatoes? Sharp blades will slice cleanly through this delicate fruit, without needing much downward force. If your knife pushes down on the tomato or the blade catches on the skin, it’s time to get your knife sharpened.

(Image credit: Kelli Foster)

4. It slips off an onion.

Still not sure? Put your knife to the onion test. A sharp knife will move straight through the skin and layers with ease. However, if your knife slips or slides off this veggie’s slick skin, it’s a telltale sign the blade needs sharpening.

5. It doesn’t pass the arm hair test.

This one is a little out of the box, but was a favorite with some of my chef instructors in culinary school. Run the knife just above your forearm, as if you’re shaving the hair on your arm. A well-sharpened knife will cut straight through hairs, but if the hairs fold over from the touch of the knife, it’s time to get it sharpened.