How to Sharpen a Santoku Knife on a Whetstone, Step by Step

Updated October 1, 2026 • 7 minute read

A santoku has a flat, double-bevel edge, which makes it one of the simpler Japanese-style knives to sharpen by hand. This guide covers the stones and grits you need, how to find and hold the angle, how to raise and remove the burr, and the mistakes that cost the most edge.

Short answer

• Use a whetstone: a medium grit (around 1000) to do the sharpening, then a finer stone (3000 to 6000) to refine the edge.
• Hold one consistent angle on every stroke. For Japanese-style double-bevel knives, sources quote about 8 to 15 degrees per side and 10 to 15 is common; follow the maker’s figure if there is one.
• Work one side until a burr forms along the whole edge, then the other side, then refine with lighter strokes.
• Rinse, dry and test on paper or a tomato. If honing keeps the edge sharp between sessions, you will sharpen less often.

What you need

• A whetstone. A combination stone with 1000 grit on one side and 6000 on the other is a practical starter, according to Kasumi’s grit guide. Two separate stones work just as well.
• A stable base. A non-slip stone holder, or a damp towel under the stone, so it cannot slide.
• A way to flatten the stone. Whetstones wear unevenly and develop dips. A flattening stone, diamond plate or sandpaper on a flat surface brings the stone back to level so the blade is not damaged.
• Water and a cloth. Use water on a water stone. Using oil on a Japanese water stone reduces its effectiveness.
• A permanent marker. Optional, but it shows you exactly where steel is being removed.
• An angle guide. Optional. A small guide or protractor helps keep the angle consistent while you build the habit.

Know your edge and your angle

A santoku is normally double-bevel: both sides of the edge are ground, so you sharpen both sides to the same angle. For Japanese kitchen knives of this type, 10 to 15 degrees per side is a commonly given range, and some sources go as low as 8. A lower angle makes a sharper edge but one that is more prone to chipping or dulling quickly; a slightly higher angle gives up a little sharpness for durability. If the maker states an angle, use it. If you are unsure, a starting point near 15 degrees is a reasonable compromise.

You do not need a protractor to check it, because the angle is just trigonometry. Measure the height of your blade at the heel, where it is tallest, from the edge to the spine. At 15 degrees the spine sits about a quarter of that height above the stone (the sine of 15 degrees is about 0.26). At 10 degrees it sits about one sixth of the height (the sine of 10 degrees is about 0.17). On a blade 45 mm tall, that is roughly 12 mm at 15 degrees and 8 mm at 10 degrees. Stacking a few coins under the spine is an easy way to hold the height steady at first.

Choosing grits

Sources draw the boundaries a little differently, so treat the ranges as approximate. For a santoku that is dull but not damaged, a 1000 grit stone followed by a 3000 to 6000 grit stone covers nearly everything.

Prepare the stone

• Check the maker’s instructions. Splash-and-go stones only need water on the surface, while many water stones work best after a soak of 10 to 15 minutes.
• Set the stone on a damp towel or holder, with the long side facing you.
• If the surface has dipped in the middle, flatten it first.
• Keep the surface wet throughout, adding water whenever it starts to dry.

Step by step

1. Mark the bevel. Colour both sides of the edge with a permanent marker. As you sharpen, the ink wears off where steel is being removed, so you can see whether you are hitting the edge evenly.
2. Set the angle. Rest the heel of the blade on the stone with the edge facing away from you and lift the spine to your angle.
3. Sharpen the first side. Push the blade forward and slightly across the stone, heel to tip, with light pressure, as though slicing a thin layer off the stone. A santoku’s edge is nearly flat, so most of it stays in contact; at the rounded tip, lift the handle slightly so the curve keeps meeting the stone.
4. Find the burr. After about ten strokes, check that the marker is coming off evenly. Keep going until a burr forms along the whole length of the opposite side. A burr is a thin strip of folded metal that tells you the stone has reached the edge. To feel it, stroke a fingertip across the edge from the spine toward the edge, never along it.
5. Sharpen the second side. Flip the knife and repeat with the same angle and pressure until a burr forms on the first side.
6. Reduce the burr. Alternate sides with fewer strokes each time and lighter pressure so the burr gets smaller.
7. Refine on the finer stone. Repeat with light pressure and fewer strokes. This removes scratches, finishes the edge and takes off the remaining burr.
8. Rinse, dry and test. Wash away the slurry, dry the blade completely and test on a sheet of paper or the skin of a tomato. The edge should bite and cut with little force.

Santoku-specific notes

• Flat edge. Because the edge is nearly flat, keeping the full length in contact with the stone is easier than on a curved chef’s knife. Slide the knife diagonally to cover the heel and the tip on each pass.
• Rounded tip. Take care at the end of the stroke. Do not drop the handle or press hard, or the tip will be ground away faster than the rest of the edge.
• Thin, hard blade. Use light pressure. A thin blade does not need force, and hard steel will chip if you twist it on the stone.
• Patterned or hollow-ground blades. Sharpening only touches the edge bevel. Keep the faces of the blade off the stone.

How often should you sharpen?

There is no universal schedule. It depends on how much you cook, what you cut on and how you store the knife. Let the knife tell you. If it slides off a tomato skin or crushes soft food instead of slicing, it needs attention. Try honing first; if that does not restore the edge, sharpen.

Common mistakes

• Letting the angle drift. Raising the handle changes the angle and rounds the edge.
• Pressing too hard. Heavy pressure wears the stone, hides the burr and can bend a thin edge.
• Skipping the burr. Without a burr you cannot be sure the whole edge has been reached.
• Leaving the burr on. It tears off in use and the knife feels dull again quickly.
• Using a dished stone, which gives an uneven edge.
• Using oil on a water stone, or letting the stone dry out while you work.
• Twisting the blade on hard foods afterwards, which chips the new edge.

Safety

• Make sure the stone cannot move before you begin.
• Keep your fingers on the flat of the blade and behind the edge.
• Check for a burr by stroking across the edge, never along it.
• Dry the knife and store it with the edge protected when you are done.

Frequently asked questions

What grit should I start with?

A 1000 grit stone handles most dull edges, and a 3000 to 6000 grit stone refines the finish. A combination stone with 1000 on one side and 6000 on the other is a practical starter.

Do I need to soak my whetstone?

Check the maker’s instructions. Splash-and-go stones only need water on the surface, while many water stones work best after a 10 to 15 minute soak.

Can I use oil on my whetstone?

Not on a Japanese water stone. Oil reduces its effectiveness, so use water.

What angle should I sharpen a santoku at?

Sources quote about 8 to 15 degrees per side for Japanese-style double-bevel knives, and 10 to 15 is a common range. Follow the manufacturer’s recommendation if you have it.

Sources

Key facts come from these pages. Practical advice and worked examples in the text go beyond them and are not quotations from them. Specifications for any one knife are the manufacturer’s to confirm.

• What angle to sharpen Japanese knives, Hasu Seizo
• Whetstone grit guide, Kasumi
• Sharpening stone, Wikipedia
• Japanese kitchen knife, Wikipedia

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