Sharpening Angle Calculator

How to use the sharpening angle calculator

First choose what you want to know.

How high to lift the spine

1. Measure the blade width from the spine to the edge, at the point where you are sharpening.
2. Enter the angle per side you want – for a flat grind with secondary bevel usually 15–20°. If you do not know your knife’s angle, match the existing bevel with the marker trick rather than grinding a new one.

The result shows how far to lift the spine above the stone, the same height as a coin stack of 1 € and 2 € coins, the inclusive angle (both sides together) with a short rating, and a table of spine heights from 10° to 25° for your blade width, with the row nearest your angle highlighted.

Angle of my Scandi bevel

1. Measure the blade thickness at the bevel shoulder – where the bevel starts, not at the spine.
2. Measure the bevel width from the edge to the shoulder line, across the flat bevel.

The result shows the angle per side with its rating, the inclusive angle, and a table of the bevel width your blade would need for 10°, 11°, 12° and 15°.

Worked examples

A 25 mm blade at 17° per side

A typical bushcraft or general-purpose knife with a flat grind is about 25 mm wide. You want a secondary bevel of 17° per side. The calculator shows:

• Lift the spine: 7.3 mm above the stone
• Coin stack: ≈ 3.1 × 1 €, or 3.3 × 2 €
• Inclusive angle: 34° – typical secondary bevel of a flat grind

The table for the 25 mm blade:

This is the same rough check as in our whetstone guide: on a blade about 25 mm wide, a spine raised about 6–9 mm gives roughly 15–20° per side. Three 1 € coins under the spine are a good first picture of 17°.

A small knife: 18 mm at 15°

A slim knife only 18 mm wide, sharpened at 15° per side: the spine goes up just 4.7 mm – a stack of about 2.0 × 1 € or 2.1 × 2 € – for an inclusive angle of 30°, still a typical secondary bevel of a flat grind. The narrower the blade, the less you lift for the same angle. That is why the same knife needs a slightly lower spine towards the tip, where it gets narrower.

A wide chopping blade: 50 mm at 22°

A heavy blade 50 mm wide at 22° per side needs the spine 18.7 mm up – about 8.0 × 1 € or 8.5 × 2 € – for an inclusive angle of 44°. The calculator rates this as the axe range – tough, made for chopping. An axe itself is usually not sharpened by lifting a spine: its convex bevel is repaired with a file and honed with a round puck in circles, as described in how to sharpen an axe or hatchet.

Measuring a Scandi bevel: 3.2 mm stock, 8 mm bevel

Your Scandi knife is 3.2 mm thick where the bevel starts, and the bevel is 8 mm wide. The calculator shows:

• Angle per side: 11.5° – typical Scandi bushcraft bevel
• Inclusive angle: 23.1°
• Bevel width for this blade thickness: 9.2 mm at 10°, 8.4 mm at 11°, 7.7 mm at 12° and 6.2 mm at 15°

The inclusive angle is calculated from the unrounded angle, which is why it shows 23.1° rather than 2 × 11.5°. A thinner blade with the same angle has a narrower bevel: 2.5 mm thickness and a 6 mm bevel give 12.0° per side and an inclusive angle of 24.0°. On a Scandi grind you do not have to hold this angle at all – lay the bevel flat on the stone and it is set. How to do that is in sharpening a bushcraft knife with a Scandi grind.

How it is calculated

Spine height. The blade forms a right-angled triangle with the stone: the edge touches the stone, the blade width is the long side, and the spine height is the side opposite the angle. So spine height = blade width × sin(angle per side). For 25 mm and 17°: 25 × 0.292 ≈ 7.3 mm. The blade thickness is ignored.

Coin stack. The spine height divided by the thickness of the coins: a 1 € coin is 2.33 mm thick, a 2 € coin 2.20 mm.

Scandi bevel. On a Scandi grind the bevel runs from the edge to the shoulder. Half the blade thickness at the shoulder is the side opposite the angle, the bevel width is the long side: angle per side = asin((thickness ÷ 2) ÷ bevel width). The inclusive angle is twice that. The bevel must be wider than half the blade thickness, or the calculator asks you to check the two measurements.

Rating bands. The note under each angle follows our sharpening guide:

• under 10°: very fine – fragile edge, push cuts only
• 10–12.5°: typical Scandi bushcraft bevel
• above 12.5° to under 15°: between Scandi and a secondary bevel
• 15–20°: typical secondary bevel of a flat grind
• above 20° to 25°: axe range – tough, made for chopping
• above 25°: very blunt angle – strong, but cuts poorly

Limits of the calculator

• Your hand is the real guide. The coin stack shows you the angle once; after that you hold it freehand. Consistency matters more than the exact number: a steady 17° beats a wobbling 15°.
• Blade thickness and grind. The spine-height formula treats the blade as thin. On a thick blade the angle that reaches the edge can come out a little steeper than the number shown. Colour the bevel with a permanent marker, take one stroke and look where the ink is gone: only at the edge means too steep, only at the shoulder too flat.
• Measuring accuracy. A ruler is only good to about half a millimetre, which moves a Scandi result by a degree or more. Use a calliper if you can.
• Convex edges. A convex knife or an axe has no single flat bevel to measure. The bands give you a target, but the technique is different.
• Tapering blades. Width and thickness change along the blade. Measure where you are sharpening.

Related reading

Start with the guide to using a whetstone for setting up the stone, then raise and remove a burr as described in the grit progression. Which grind your knife has – Scandi, flat or convex – is explained in knife grinds. For axes and hatchets see our guide to choosing and using an axe, for sloyd and hook knives the overview of carving tools. Oil, rust protection and storage after sharpening are covered in tool care. Planning a longer trip with phone and headlamp as well? The power bank calculator sizes the battery that goes in the pack next to your stone.