This post has been updated since it was first posted in August 2012.
The vast majority of people can’t tell a dull knife from a sharp knife. People automatically assume that if a knife can cut, it’s sharp.
Unfortunately, that’s not always the case.
A dull knife will usually cut, but it requires much more force and energy than if you’re cutting with a truly sharp knife. So how can you tell if a knife is truly sharp? Here are a few ways to determine the sharpness of a blade.
Let us know your sharpness tests in the comments.
1. The Paper Test
Probably the most tried and true method is the good ol’ fashioned paper test. Grab a piece of paper, hold it between your fingers, and slide the knife downward. If it’s sharp, it will cleanly and easily slice the paper with just the weight of the knife. If it’s dull, it will usually be ragged or slip right off. This test also allows you to find any jagged or missed spots if you cut the whole length of the edge on a single stroke.
For an even better test of a blade’s sharpness, use a piece of magazine paper. Paper from a magazine is exceptionally thin and slick, which makes it even more difficult for a knife to slice through. According to Mike Vellekamp (who used to work at Spyderco before his current venture of V Nives), Sal Glesser used to make them use paper from National Geographic magazines. Phone book paper is an even tougher test, and toilet paper is the toughest.
Yet another variation fo the paper test is to fold the paper in half so it has a rounded edge. Cut the paper along the rounded edge and if it’s sharp, it will catch and cut the page.
Here’s a good clip from the legendary Bob Kramer on the paper test.
2. The Shaving Test
If you’ve ever watched knife reviews on YouTube, you’re probably familiar with the next test. It involves running the knife along your hair (usually your arm hair) and watching the little hairs get lopped off as the blade comes gliding through. Any hairs that fold under will indicate that the blade is not up to snuff.