Sharpening Grits Explained

Grit is the most confusing number in sharpening, and almost all of the confusion comes from one fact: there is no single grit standard. A waterstone marked 1000, a sheet of sandpaper marked 1000 and a diamond plate marked with a micron figure are describing three different surfaces, and the numbers do not convert cleanly. Once you know why, the whole subject stops being intimidating.

The good news is that you do not need to master the conversion tables. You need to know which band a stone falls into — coarse, medium, fine or polishing — and you need to buy all your stones from one system so the numbers stay comparable. That is most of the battle.

Why the same number means different things

A grit rating is an attempt to describe the size of the abrasive particles on a surface. Different industries measure that size differently. Some sieve the particles through a mesh and count the openings per inch; some measure the average particle diameter directly in microns; some use a statistical cut-off that discards the largest particles. Each method produces a different number for the same actual grit.

The divergence is small at coarse grits and grows large at fine ones. At 220 the systems more or less agree. By the time you reach the polishing range they are wildly apart, which is why a “1000 grit” sandpaper and a “1000 grit” Japanese waterstone are not interchangeable and do not leave the same scratch pattern.

The four systems you will meet

JIS (Japanese Industrial Standard).The scale printed on almost every waterstone sold for woodworking. Higher number is finer. When a woodworker says “a 1000 stone” without qualification, this is the scale they mean, and it is the one to standardize on.

ANSI / CAMI.The North American scale used for coated abrasives — sandpaper. Higher number is finer. A CAMI grit is coarser than the same JIS number once you get past the middle of the range, which matters if you sharpen on sandpaper.

FEPA-P.The European sandpaper scale, written with a “P” prefix (P400, P1000). It tracks CAMI closely at coarse grits and pulls away at fine ones. If a sheet says P800 rather than 800, it is FEPA.

Micron.Not a grit number at all but the actual average particle size in micrometres, and the only figure that is directly comparable across products. Smaller is finer. Diamond plates, lapping films and honing compounds are often rated this way, and it is the honest unit — a 3-micron diamond and a 3-micron film are genuinely similar. When you want to compare two products from different systems, convert both to microns in your head.

A rough cross-system table

Treat every row below as approximate. Conversions between grit systems are estimates, the published figures vary from one source to the next, and manufacturers within a system are not perfectly consistent either. The point is not the exact numbers; it is the shape of the relationship.

Read across a row and the pattern is clear: to reach the polishing range on sandpaper you need a far lower-looking number than on a waterstone. That is exactly the trap that makes people think their sandpaper edge is coarser than it is. If you sharpen on paper, the grit progression works differently, and the scary sharp method page walks through a progression that actually lands where you want it.

What each band is actually for

Coarse (under ~400 JIS): repair only. Reprofiling a chipped edge, grinding a new bevel angle, or flattening another stone. A coarse grit removes metal fast and leaves deep scratches you then have to work out. You should not touch it in a normal sharpening session.

Medium (400–800 JIS): setting a bevel. Establishing a fresh bevel or recovering an edge that has gone properly dull. Useful, but skippable if your edge is only lightly worn. Many people move straight from repair to the working grit and never own a dedicated medium stone.

Fine (1000–2000 JIS): the working grit. This is where a sharp edge is actually created. If you own one stone, own this one. A 1000 leaves an edge that will plane and pare cleanly, and for a lot of joinery it is genuinely all you need.

Polishing (4000–8000 JIS): keenness and shine.Takes a sharp edge to a keen one and leaves a bevel that reflects. Worth having for paring and for finish planing, where the difference shows in the surface. Above 8000 the returns fall away fast for woodworking — a charged strop achieves most of what a 12000 stone does, for a fraction of the cost.

What grit for repair versus honing

These are two different jobs, and conflating them is the most common beginner mistake. Repair is occasional and coarse: you reach for it when something is chipped, when you are changing an angle, or when a neglected tool has no real bevel left. It is measured in minutes of grinding.

Honing is the routine act of restoring a sharp edge to a tool that was already close. It happens at the working and polishing grits only, it should take a minute or two, and it should never involve a coarse stone. If you find yourself starting every sharpening session on a 220, something is wrong — either you let the edge get far too dull, or you are grinding a new bevel each time instead of maintaining the one you have. A honing guide and a repeatable angle fix that; see the sharpening starter kit for the full setup.

How many stones you actually need

Fewer than the internet will tell you. A twelve-stone progression is a hobby, not a requirement. The honest minimums:

• One stone. A 1000 waterstone plus a strop. The stone makes the edge, the strop refines and maintains it. This sharpens every edge tool in a normal shop.
• Two stones.A 1000 and a 6000, or the two faces of a single combination block. Working grit and polishing grit — the standard first purchase and the one most experienced sharpeners settle back to.
• Three, at most. Add a coarse stone or a coarse diamond plate for repair. That plate can also flatten your waterstones, so it earns its place twice over.

Beyond three, you are buying grits that overlap so closely that no edge can tell the difference. The money is better spent on the stones themselves — the best sharpening stonesroundup ranks them — and on the maintenance kit that keeps them flat. If you are still deciding between a waterstone and a plate before you worry about grit at all, start with waterstones versus diamond stones, because the medium you choose changes which grit numbers you will even see.