There are plenty of ways to test sharpness: The classic tomato slice, the paper test, rope cutting — knife enthusiasts have come up with all sorts of ways to anecdotally confirm their edge is honed.
But to truly compare and rate a blade’s performance, we needed to get a little more scientific.
So, we spent over $250 to get our hands on a scientific sharpness tester for our knife reviews: The Edge-On-Up PT50A Sharpness Tester is a certified, high-resolution, gram-scale tester that provides accurate sharpness ratings for any blade. We’re going to use this testing scale with our own repeatable, standardized edge retention testing.
With these two tests, we can rate a knife’s cutting ability against its advertised hardness, steel composition, edge angle, and grind. We’ll be able to tell how well a knife holds up to its cost and expected performance, relative to its own construction and other blades.
How The Sharpness Tester Works
At the center of the tester lies the all-important testing media: A thin, synthetic wire placed under tension, that a blade must cut through. This “DoubleX+” wire is certified to ensure consistent, fair, accurate results.
The amount of force required to cut through the wire provides the sharpness score. That force is measured in grams by the PT50A scale.
The resolution of the PT50A’s scale is 1 gram. It records the cutting force applied 5 times per second, providing high accuracy. Edge-On-Up’s less expensive testers are made for occasional, personal use. They provide resolutions of 5 grams (the “PT50B” model) and 25 grams (the “PT50C” model).
Prepping the Tester
The synthetic test wire is housed inside the machined steel test block.
The wire is fed through two channels machined into the top of the measurement block. Tension is provided by two set screws and a metal washer.
The metal washer prevents over-tightening the test media, ensuring the same amount of tension is provided for accurate test results.
A machined aluminum fulcrum with a magnetic base supports the blade’s edge as it cuts through the media, via a channel cut into the top.
For faster and easier testing, the Edge-On-Up can be used with prefabricated aluminum “speed clips.” Each clip comes with test wire fitted between two prongs. The clips rest atop an aluminum block for the gram scale. These speed clips are not certified, and sharpness tests using these clips may be less accurate.
For our knife reviews, we’re only using the certified test wire, seated within the steel measurement block.
Test Results & Sharpness Ratings Compared
The BESS Universal certification provides the expected test results (sharpness ratings) for common types of blades when used with the Edge-On-Up tester:
- Double-edged razor blades measure between 50 and 80 grams.
- New utility blades (box cutters) measure between 150 and 200 grams.
- New blades on common knives measure between 250 and 375 grams.
- An edge is dulled and needs sharpening between 400 and 800 grams.
- Severely rolled edges usually measure between 900 and 1375 grams.
- A damaged, bent edge measures between 1400 and 1525 grams.
- Edges measuring 1200 grams or more require grinding (re-profiling).
If you’re trying to get the most sharpness possible out of your own knife, check out our guide to edge angles.
