Knife Edge Geometry and Bevel Angles: Sharpness, Retention and CATRA Testing

Two knives can be made from the same steel, hardened to the same HRC, and cut completely differently. The reason is geometry: the angle of the bevel, how thin the steel is just behind the edge, and how the grind transitions from edge to spine.

This guide covers the geometry that matters, the ambiguity in how it is specified, and the standard test methods used to prove a knife actually cuts.

The ambiguity that ruins specifications: per side or inclusive

When someone says "a 15 degree edge", they may mean one of two very different things:

• 15° per side — the total included angle is 30°.
• 15° inclusive — 7.5° per side.

A knife at 15° per side is roughly twice as stout at the apex as one at 15° inclusive. The cutting difference is dramatic. So the single most useful thing a buyer can do is write "per side" or "inclusive" explicitly, every time, and require the supplier to confirm which they measured.

For context, indicative ranges used in the industry:

Geometry beyond the apex angle

The included angle is only one of three variables. The other two explain why two 17°-per-side knives feel different:

This is why "thinning" a knife is a separate operation from sharpening it. Sharpening restores the apex; thinning removes material behind the edge to restore cutting efficiency. A blade sharpened many times without thinning becomes a knife that is technically sharp but no longer slices.

The grind types

Sharpness: what is actually being measured

"Sharp" is not one property. Three different things get measured, and they answer different questions:

• Edge sharpness (apex quality) — how fine the apex is. Measured with instruments such as the BESS scale, which reports the force in grams required to sever a standard test medium. Lower is sharper. A typical production kitchen knife sits in a mid range of that scale, a razor at the low end, and a dull knife high up. Absolute numbers vary between models of instrument, so use the scale for comparison within one test setup.
• Cutting ability through a medium — how much effort it takes to complete a cut in real food. This is where edge thickness behind the apex dominates, and it is why two equally "sharp" knives can perform differently on an onion.
• Edge retention — how long the knife keeps cutting. This is the property most relevant to a buyer, and the one most often asserted without evidence.

CATRA and standardised cutting tests

Edge retention is normally proven with a standardised machine test rather than opinion. The best known is the CATRA test, developed by the Cutlery and Allied Trades Research Association in the UK. A blade is drawn repeatedly through a standardised abrasive test medium under controlled load and speed, and two figures are reported:

Because the medium, load and motion are fixed, results are comparable between blades and between batches from the same blade profile. That comparability is the whole point: it converts "this holds its edge well" into a number a buyer can put in a specification and a supplier can be held to.

If your programme is large enough to justify it, ask whether the factory has CATRA data for the model, or has run a defined cutting test of its own with a stated protocol. If the answer is a demonstration on a tomato in a video, you have a marketing asset, not evidence.

How to verify geometry on a sample

1. Measure the bevel angle. A goniometer or a simple optical measurement on a cross-section gives the real angle. Do not accept a spec sheet figure for the sample in your hand.
2. Check the angle is consistent along the blade. Measure near the heel, mid-blade and near the tip. Variation suggests manual grinding or setup drift.
3. Check for symmetry. Both sides should match unless a single-bevel design was specified.
4. Feel for a burr or a wire edge. A residual burr gives a knife that feels sharp and dulls in minutes — a common result of over-grinding at the polishing stage. See AQL inspection for knife orders for where to place this in an inspection brief.
5. Cut something standard. A ripe tomato and a sheet of newspaper are crude but consistent. Cutting feel between two samples tells you a lot before any instrument does.

What to specify

• Bevel angle, explicitly per side or inclusive.
• Grind type.
• Blade thickness at the spine and, if you can get it, behind the edge at a defined distance.
• Tolerance on the angle, for example ±1°.
• Whether a micro-bevel is permitted, and at what angle.
• Sharpness acceptance criterion, by an agreed method.

Geometry is the cheapest performance lever available — it costs nothing in steel and everything in process discipline. A factory that can hold a thin, even bevel consistently is worth more than one with a longer equipment list. Our OEM and ODM process starts by fixing exactly these numbers before tooling, and our manufacturing page shows where grinding sits in the line.

FAQ

Is a thinner edge always sharper?

It cuts with less resistance, but a thinner edge is weaker and dulls or deforms faster. Thin and hard is the combination that chips. Geometry, hardness and use have to be chosen together.

What angle should a general purpose chef knife be?

For a Western-style chef knife used by a broad retail audience, 15–20° per side is the usual range. Lower for a premium thin blade used carefully, higher for anything that will meet bone. See hardness for the matching HRC choice.

Can I ask a factory for CATRA data?

You can, and a serious factory will either have it or will tell you what testing it does have. Both answers are useful. What is not useful is a performance claim with no test behind it.

Does a serrated edge need this analysis?

The teeth protect the apex, so the included angle matters less. For serrated blades the tooth geometry, the depth of the scallops and the sharpening method are the variables — see our specialty knives range for examples.