You bought one Japanese knife. Now you are looking at a wall of stones numbered from 220 to 12000, and every guide wants to sell you three of them.
Buy one stone around #1000. That is the answer for almost everyone reading this, and the rest of this page is about when it stops being the answer.
The number is not a certified figure
Start here, because it changes how you read every listing.
There is a Japanese Industrial Standard for abrasive grit — two of them, in fact, both established in 2017. What they standardize is the size distribution of loose abrasive grain. Not the finished stone. Not the number printed on its box.
Nothing we could find establishes that a consumer sharpening stone’s printed number is certified or audited against that standard, and no JIS-mark scheme for kitchen whetstones exists.
But do not swing to the other conclusion either. One major maker publishes its own micron figure beside every grit it sells, and those figures track the JIS series almost exactly up to #8000. The numbers are not invented. They are a convention that mostly holds — which is a different thing from a certification, and worth knowing before you pay a premium for a decimal point.
Where it actually breaks: the same number, twice the grit
This is the part that costs people money.
The body that develops the ANSI abrasive standards states it plainly: the same size number can refer to very different sizes depending on which standard is being used. Its worked example is exactly the one that matters here — a JIS 600 averages 18.5–21.5 microns, while a FEPA F600 averages 8.3–10.3.
We did not take that on one source. A Japanese abrasive manufacturer publishes F600 at 9.3 ± 1.0 µm, which lands inside the ANSI body’s range for the same designation. Two independent bodies, the same answer.
So a Japanese # number and a European F number are not interchangeable, and any conversion chart presenting them as equivalent is doing you harm. Buy within one system, or read the micron figure instead of the number.
And above #8000, the scale simply stops
The JIS microgrit series runs to #8000 and ends there.
Stones are sold at 10000, 12000, 16000, 30000. Those numbers sit outside the standard’s series entirely.
You can watch a manufacturer arrive at that boundary. One maker’s own product table gives a micron class for every stone from 320 through 8000 — and for its 10000 and 16000 stones prints no micron figure at all, substituting a word. The maker stops publishing a number at exactly the point the standard stops defining one.
The category words are not specifications either
Coarse, medium, finishing sound like grades. They are trade vocabulary, and makers do not agree.
#1000 is labeled four different ways across current catalogs we read: one calls it medium-finishing, one calls it medium, one sells it as a medium stone and another line from the same company sells the same grit as a medium-coarse.
And one maker contradicts itself at a single number. Its deluxe #6000 is sold as super-finishing; its finishing series, also at #6000, is sold as finishing. Same company, same grit, two categories.
If you have read our knife article, this will sound familiar. No Japanese Industrial Standard sets blade length by knife name either. The pattern is the same: a word that sounds like a specification, doing the work of a category label.
JBJ'S TAKE
Read the micron figure. Ignore the adjective.
A number is at least a convention. "Medium" is one company's shelf label, and the company down the road uses it for something else.
So when a maker publishes microns, that is the figure to buy on. When it doesn't — that is information too.
So what do you actually buy
Here is where most guides go quiet, and we said we would not.
One stone, around #1000. For a home cook with one double-bevel knife that is not chipped, this does the whole job. It removes enough metal to restore an edge and leaves a finish that cuts vegetables and protein perfectly well.
A flattening plate, bought at the same time. This is the accessory the field leaves out of the price, and it is not optional. Three separate manufacturers state that a stone must be kept flat to sharpen correctly, and one warns plainly that a stone worn hollow in the middle is dangerous, because the edge catches. A dished stone does not sharpen worse — it sharpens wrong.
Nothing else, yet.
You need a coarse stone only if you have actually chipped the blade. If you bought the knife recently and have not dropped it on tile, you do not have that problem, and a coarse stone will spend years in a drawer. You need a finishing stone only once you can reliably produce a good edge on the #1000 and can tell that you want more — which is a real point, and it arrives later than the shop suggests.
One maker does publish a beginner recommendation, and we are noting that because we expected to find nobody would. It suggests a #1000 plus a #5000, or a single #1500 if you want one stone. That is a manufacturer’s recommendation for its own range, which does not make it wrong — but it is not a neutral source, and no neutral source exists.
JBJ'S TAKE
Every party who will tell you what to buy also sells stones.
That is the actual gap. Not silence — nobody is hiding anything. There is simply no disinterested authority on how many stones a home cook needs.
JbJ sells none, so: one stone and a flattener. Add the second when the first one stops being the limit. Most kitchens never get there, and that is fine.
Water, and the one instruction that is genuinely per-product
There is no universal soaking time, and pages that give you one are guessing.
The makers differ, legitimately, because the stones differ. One states that its stones do not need soaking — except five or six minutes before first use — and caps immersion at thirty minutes, warning that longer softens the stone. Another asks for ten to twenty minutes, until the bubbles stop.
Both are correct about their own products. Neither transfers.
So the instruction is: read the box your stone came in. That sounds like a non-answer and it is the only honest one. We are also not printing the specific soaking times circulating for three other well-known brands, because we went to those manufacturers’ own pages and the figures are not there.
Two things not to carry over from elsewhere
Search 砥石 安全 in Japanese and you will land on industrial safety law — mandatory trial-running periods, guards, ring tests, protective equipment, formal worker training. None of it applies here. That regime governs powered grinding wheels, and the companies publishing it make industrial cutting discs, not kitchen bench stones.
Natural stones do not have a grit number. They are not manufactured to one, so any “equivalent grit” printed next to a natural stone is an estimate someone made, not a measurement. We could not find an official definition of natural versus synthetic stones at all, and no whetstone appears among Japan’s designated traditional crafts in the lists we were able to check — including Kyoto’s own list of seventeen, in the prefecture most associated with natural finishing stones.
Before you go
Buy the #1000. Buy the flattener. Keep the box, because it has the soaking instruction on it and no website can tell you that reliably.
And if you are shopping outside Japan, check whether the number on the front is a JIS number or an F number before you assume it matches the one you already own.
Checked 2026-09-02. Grit standards and their scope come from the Japan Standards Association’s published records; the cross-standard particle sizes from UAMA, which develops the ANSI B74 abrasive standards, corroborated against a Japanese abrasive manufacturer’s own published figures; the grit-to-micron table, category labels, soaking limits, flattening guidance and beginner recommendation from the manufacturers’ own official documentation; craft-designation status from the national promotion body and Kyoto City. The full texts of the relevant JIS standards are paywalled, so their scope statements were read and their clause text was not. No retailer, marketplace, review site or sharpening blog was used as a source. No price and no product model appears on this page.
