How to Test If Your Knife Is Sharp

A dull knife isn’t just frustrating, it’s dangerous! Dull blades require more pressure and can slip instead of slicing. This means less control and a higher chance of the knife slipping off whatever you’re cutting and onto your hand.

The good news is that there are four simple tests you can do to test knife sharpness at home: the paper test, the tomato test, the thumbnail test and the basil test.

Here’s how each one works, what it’s actually measuring and what ‘sharp’ should look like if you’re testing a GLOBAL knife.

The Paper Test

How to do it: Hold a sheet of paper by one edge, letting it hang free. Without any sawing motion, draw the knife down through the paper in one smooth stroke.

What it tells you: This is the classic ‘how sharp is my knife edge’ test. Paper offers almost no resistance, so any snagging, tearing or folding means the edge is not sharp enough.

What counts as sharp for a GLOBAL knife: GLOBAL blades are ground thin with a 15 degree edge on each side. A properly sharpened GLOBAL should glide through paper in one clean stroke, leaving a smooth cut edge. If you hear a ripping sound or the paper bunches up, the edge has lost its sharpness and its time for a few passes on a whetstone, honing steel or pull-through sharpener.

The Tomato Test

How to do it: Rest a ripe tomato on a cutting board and try to slice through the skin using only the weight of the blade, no downward pressure or sawing.

What it tells you: Tomato skin thin but smooth which makes it perfect for this test. The test measures whether a blade edge can immediately cut through the surface on contact, with no additional effort or pressure.

What counts as sharp for a GLOBAL knife: A GLOBAL knife should sink into the tomato skin as soon as it touches it, then it should glide through to the board in one motion, producing a clean slice with no crushed or torn flesh. If you find yourself having to press down or rock the blade to break through the skin, the edge is due a sharpen.

The Thumbnail Test

How to do it: Exercise caution with this method! Rest the edge of the blade LIGHTLY on your thumbnail at a shallow angle and VERY GENTLY push to see if there is a bite. Never slide sideways and do not press too hard - this is a feel test, not a cutting test!

What it tells you: A sharp edge will bite and catch on the nail immediately whereas a dull edge will slide on the surface without gripping. This test is popular because it’s fast and doesn’t need any setup, just be careful!

What counts as sharp for a GLOBAL knife: The blade should grab the nail immediately and hold its position without sliding across the surface. If it slides, that’s a sign your blade needs honing or sharpening.

The Basil Test

How to do it: Stack a few basil leaves and slice through them in one clean pass. Set the cut leaves aside and check back after a few minutes.

What it tells you: Basil is one of the most sensitive ingredients in the kitchen as its leaves bruise and oxidise when the cell walls are crushed rather than cleanly sliced. When the leaf is crushed, it releases enzymes that turn the edges brown making it a great indicator for knife sharpness. A cut may look fine at first but basil will indicate if it was a dull edge.

What counts as sharp for a GLOBAL knife: A properly sharpened GLOBAL Japanese knife should glide though basil leaves with almost no resistance, leaving bright green, crisp edges. Check the cut edges a few minutes lates, they should still look vibrant. If the basil has visibly bruised or browned along the cut, the edge was crushing rather than slicing and you knife needs sharpening.

Next Steps…

If you’re knife fails one of these tests, it’s time to sharpen your knives and imporve your kitchen knife safety. GLOBAL Japanese knives are designed with a thinner blade profile than most Western knives which means they respond well to regular honing and sharpening on a whetstone, pull-through sharpener or sharpening steel. Check out our blogs on knife sharpening for top tips and advice on the best maintenance for keeping the razor-sharp edge.