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Bevel angle calculator

The included angle of a flat grind from two calliper measurements, with the grind ratio that is easier to hold in your head at the belt. It tells you what you have ground, not what you should grind.

The question this answers: “The stock is 3.5mm and I have ground a 15mm bevel. What angle is that, and how does it compare with the one I ground last time?”

At the spine, above the bevel.

Measured up the face of the blade from the edge to the top of the grind, not along the edge.

What you are leaving at the edge before it goes to stones. Zero gives the geometry of a fully closed grind.

Result

Per side
6.09°
Included angle
12.18°
The figure usually quoted when knives are compared, and it is twice the per-side angle. Sharpening guides are often marked per side, which is where the factor of two goes missing.
Grind ratio
9.4 : 1
Bevel width against the rise. Easier to hold in your head at the grinder than an angle, and it is what you are actually watching.
Rise per side
1.6 mm
Half the stock, less half the edge you are leaving before sharpening.

Worth knowing about this answer

  • This is the angle you have ground, not the angle you should grind. What a blade wants depends on the steel, the heat treatment and the job, and no calculator can know those.
Show the working
  1. Rise per side(3.5 − 0.3) ÷ 21.6 mm
  2. Per-side angleatan(1.6 ÷ 15)6.09°
  3. Included6.09 × 212.18°

Per side: 6.09°. Included angle: 12.18°. Grind ratio: 9.4 : 1. Rise per side: 1.6 mm

How it works

Each side rises by half the stock thickness less half of whatever edge remains, over the width of the bevel. The arctangent of that gives the per-side angle and doubling it gives the included angle usually quoted when blades are compared.

What it assumes

  • A flat grind. A hollow or convex grind has a curved bevel and no single angle, and this will describe the chord rather than the geometry.
  • A bevel of constant height along the blade. Distal taper and a curved edge both change the local angle, so this describes the section you measured.
  • That the bevel width is measured up the face. Measuring along the edge of a curved blade is the commonest way this comes out wrong.

Where it stops being reliable

  • It cannot tell you what angle to grind. That depends on the steel, its heat treatment and what the knife is for — a thin geometry in a hard steel chips where a thicker one would roll, and the trade is a judgement rather than a calculation.
  • It says nothing about the sharpening bevel, which is a separate and steeper angle applied at the very edge.
  • It is not a heat-treatment, steel-selection or edge-retention tool. Those are properties of a specific steel and belong to its maker’s data.

Runs entirely in your browser — nothing you type is sent anywhere. Last reviewed 2026-08-19. More on Knifemaking.