Four standards use the same numbers and mean different things by them. A stone marked #1000 can carry particles of 4.5 micrometres or 18.3, depending on which standard the maker used. The listing rarely says which.
| Grit | FEPA-F | ANSI | JIS R 6001 | FEPA-P |
|---|---|---|---|---|
| #400 | 17.3 ±1 | 22.5 | 40 | 35.0 ±1.5 |
| #500 | 12.8 ±1 | 18 | 34 | 30.2 ±1.5 |
| #600 | 9.3 ±1 | 14 | 29–30 | 25.8 ±1 |
| #800 | 6.5 ±1 | 12 | 20 | 21.8 ±1 |
| #1000 | 4.5 ±0.8 | 7.8 | 14–16 | 18.3 ±1 |
| #1200 | 3.0 ±0.5 | 5.5 | 12–13 | 15.3 ±1 |
| #1500 | 2.0 ±0.4 | — | 10 | 12.6 ±1 |
| #2000 | 1.2 ±0.3 | — | 8–9 | 10.3 ±0.8 |
| #2500 | — | — | — | 8.4 ±0.5 |
| #3000 | — | — | 5 | 7 |
| #4000 | — | — | 3 | — |
| #5000 | — | — | — | 5 |
| #6000 | — | — | 2 | — |
| #8000 | — | — | 1–1.2 | — |
Open the number printed on your stone. If the listing named a standard, read that row of the table above instead — most listings do not.
The coarsest reading is 2.3 times the finest.
Nothing on the stone tells you which standard was used. Until the maker names one, #400 is not a figure you can compare against another maker's #400.
The coarsest reading is 2.7 times the finest.
Nothing on the stone tells you which standard was used. Until the maker names one, #500 is not a figure you can compare against another maker's #500.
The coarsest reading is 3.2 times the finest.
Nothing on the stone tells you which standard was used. Until the maker names one, #600 is not a figure you can compare against another maker's #600.
The coarsest reading is 3.4 times the finest.
Nothing on the stone tells you which standard was used. Until the maker names one, #800 is not a figure you can compare against another maker's #800.
The coarsest reading is 4.1 times the finest.
Nothing on the stone tells you which standard was used. Until the maker names one, #1000 is not a figure you can compare against another maker's #1000.
The coarsest reading is 5.1 times the finest.
Nothing on the stone tells you which standard was used. Until the maker names one, #1200 is not a figure you can compare against another maker's #1200.
The coarsest reading is 6.3 times the finest.
Nothing on the stone tells you which standard was used. Until the maker names one, #1500 is not a figure you can compare against another maker's #1500.
The coarsest reading is 8.6 times the finest.
Nothing on the stone tells you which standard was used. Until the maker names one, #2000 is not a figure you can compare against another maker's #2000.
Nothing on the stone tells you which standard was used. Until the maker names one, #2500 is not a figure you can compare against another maker's #2500.
Nothing on the stone tells you which standard was used. Until the maker names one, #3000 is not a figure you can compare against another maker's #3000.
Nothing on the stone tells you which standard was used. Until the maker names one, #4000 is not a figure you can compare against another maker's #4000.
Nothing on the stone tells you which standard was used. Until the maker names one, #5000 is not a figure you can compare against another maker's #5000.
Nothing on the stone tells you which standard was used. Until the maker names one, #6000 is not a figure you can compare against another maker's #6000.
Nothing on the stone tells you which standard was used. Until the maker names one, #8000 is not a figure you can compare against another maker's #8000.
FEPA separates grit for coated abrasives from grit for bonded abrasives. Sharpening stones fall under the second, FEPA-F. Sandpaper uses FEPA-P. A maker quoting a number without saying which one has told you almost nothing, and the two scales are furthest apart exactly where sharpening stones live.
Charts that place an ANSI number beside a JIS number are lining up the nearest numbers, not equal particle sizes. Reading across a row and treating the result as a conversion is the most common way these charts are misused.
Two stones with the same particle size can cut differently. The spread of sizes around the average matters, and so does the shape of the particles, how much of each the binder exposes, whether they fracture under pressure, their hardness, and what they are made of. A tight distribution is what a good stone is selling.
Japanese natural stones are graded as ara-to, naka-to and shiage-to. The classes are broad and do not convert to a grit number.
The figures come from published conversion tables from European abrasives suppliers, cross-checked against Japanese sharpening references. The two European tables agree exactly, which may mean they share a common origin rather than confirming each other independently. The JIS column also matches Japanese sources to within rounding, which makes it the best-supported column here. The JIS and FEPA standards themselves are paid documents and have not been read directly. Ranges are given wherever sources round differently. Figures for diamond and CBN abrasives follow a different standard, JIS B 4130, and are deliberately excluded.