Sandpaper grit guide: progressions by project and abrasive type

01What does a sandpaper grit number mean?

A grit number describes the average size of the abrasive particles on the paper or disc: the higher the number, the smaller the particles and the finer the scratch they leave. Two grading scales are in common use on coated abrasives. CAMI is the United States scale and uses plain numbers. FEPA is the European scale, and its grades carry a P prefix to tell them apart from CAMI grades. The FEPA P-grade scale is also the basis of ISO 6344. American grain sizing is published by ANSI: the University of Illinois engineering standards list records ANSI B74.12 as the Specification for the Size of Abrasive Grain for grinding wheels, polishing and general industrial uses, with a 2018 edition. That title covers bonded and polishing grain; the separate US grading standard for coated abrasives could not be confirmed from a fetched page, so it is not named here.

Because both scales describe particle size, a micron figure is the reliable way to compare them. At the grades most people use on wood they line up well: P180 and CAMI 180 both average about 78 µm. A full side-by-side table lives on the CAMI to FEPA grit conversion chart, and the CAMI and FEPA section further down this page covers where the two scales part company.

Grit is one of three choices on any sanding disc. The other two are the abrasive grain, which decides how the particles cut and wear, and the backing and attachment, which decide whether the disc fits the sander. This guide covers the first two; disc sizes and hole patterns are covered in the guide to sanding disc sizes and hole patterns.

02What grit sequence should you use on bare wood?

On bare wood, start at the finest grit that removes the defects and work up through the sequence 60, 80, 100, 120, 150, 180, 220 grit, which Woodcraft gives as the standard wood progression. Woodcraft's advice is to work through every grit level. Klingspor's guidance is a little more lenient, allowing a skip of no more than 1 grit step. This guide follows both: take every grit where you can, and never skip more than Klingspor allows.

The starting grit depends on the surface, not on habit: Woodcraft's rule is to start at the finest grit that removes the defects. Starting coarser than necessary only adds scratches that every later grit then has to remove. The stopping grit depends on the finish, covered in the next section.

The table below sets out the sequences and stopping points that Woodcraft, General Finishes and Klingspor publish for common wood jobs.

03How do you sand through a grit progression, step by step?

The steps below follow a typical bare-wood progression with a random orbital sander, from first grit to the last pass before finish. Speeds and pressures come from Family Handyman, Popular Woodworking and Woodsmith.

1. Pick the starting grit. Choose the finest grit in the 60, 80, 100, 120, 150, 180, 220 grit sequence that will remove the worst mark on the surface.
2. Fit the disc cleanly. Clean the pad, centre the disc and line its holes up with the pad's dust ports so extraction works. Connect a vacuum if the sander takes one.
3. Sand slowly and lightly. Move the sander at about 1 in per second with light pressure of about 2–4 lb, roughly the weight of your arm. Family Handyman suggests overlapping each pass by about 50% on large surfaces.
4. Keep the pad flat. Do not tilt the sander to chase a scratch with the pad edge; tilting leaves gouges and rounded edges.
5. Clean the surface between grits. Vacuum or wipe the work before changing grit, so loose coarse particles are not dragged around under the finer disc.
6. Move up one grit and repeat. Sand until the previous grit's scratches are gone, then change to the next grit in the sequence.
7. Stop at the grit your finish needs. Stop at about 180–220 grit before stain, or follow the finish maker's figure, then remove the dust before finishing.

04Which grit should you stop at before stain or finish?

Stop at about 180–220 grit before staining, because finer sanding closes the wood pores and stops stain soaking in evenly. Woodcraft and General Finishes both give that range.

A common belief is that sanding bare wood to a very fine grit always gives a better finish. It does not: sanding too fine closes the grain, so stain and some finishes cannot soak in evenly, and the right stopping point depends on the product. General Finishes gives these figures for its own finishes, which work as general grit advice:

• Before an oil-based stain: 120 then 150 grit.
• Before a water-based clear topcoat on raw wood: 120 then 150 or 220 grit.
• Before an oil-based clear topcoat: up to 150 grit.
• Between topcoats: a fine foam sanding pad of 220–320 grit, then remove the dust.

General Finishes also separates closed-grain woods such as cherry, maple and pine from open-grain woods such as oak and ash for water-based stains, with the open-grain woods taken a grit further; the table above gives both sequences.

Foam pads carry their own labels. General Finishes says a pad's grit does not match a paper's: by its account, 220 pad = 400 paper, and pad names and grits differ between brands. When sanding between coats of paint or lacquer, a stearated abrasive is usually the best choice, because the coating resists clogging.

05What happens if you skip grits?

Skipping grits leaves deep scratches that the finer grit cannot easily remove, and those scratches show up once stain or lacquer goes on: stain collects in them and looks darker. Mirka and a Klingspor column in Wood Shop News both describe the same effect.

The time saving is also false. Klingspor's example is a jump from the coarse end of the sequence straight to 220 grit: it uses about double the 220 paper that a full sequence would need, plus extra sanding time, because a fine grit is not designed to remove a coarse scratch. Skipping saves no abrasive and still risks visible lines.

Skipped grits are the first cause listed in the guide to sander swirl marks, ahead of too much pressure, moving too fast and a worn pad. If marks appear only after finishing, the progression is the first thing to check.

06How do CAMI and FEPA grits compare?

CAMI and FEPA numbers match closely up to about 220 grit; above that, the scales diverge and equivalents are only approximate. Fine Woodworking and PACE Technologies both put the split at that grade.

In the coarse-to-medium range used on bare wood, FEPA papers are slightly coarser and cut a little faster than CAMI papers of the same number, according to Fine Woodworking and Klingspor's micron tables. At 220 grit the two are nearly identical: P220 averages about 65 µm and CAMI 220 about 66 µm.

Above that point a common mistake is to treat the numbers as interchangeable. P400 averages 35 µm, which is close to CAMI 320, not CAMI 400. At the fine end, matching CAMI 600 takes P1000 to P1200 paper, and CAMI 800 is close to P1500. Fine Woodworking adds that FEPA paper has a greater share of particles close to the stated size, so its scratch pattern tends to be more uniform. Very fine abrasives are often graded directly in microns instead.

The practical rule is to read the prefix. Mirka's Abranet discs, for example, are sold in P-grades such as P120, while Diablo and Bosch list plain grit numbers. The difference is small at wood-sanding grades but matters once a progression goes finer, where the conversion table is needed. The table below pairs each CAMI grade with its nearest FEPA grade by average particle size.

07Which abrasive grain should you choose?

For bare wood and most steel, choose aluminium oxide, the general-purpose grain; switch grains only for heavy stock removal, finishing coats, or hard and unusual materials. Coated abrasives use 4 grain types: aluminium oxide, silicon carbide, zirconia alumina and ceramic aluminium oxide.

• Aluminium oxide has blocky grains with sharp edges that leave a fine, even scratch, which suits low-pressure orbital discs and hand sheets.
• Silicon carbide is very hard but brittle and wears quickly. It is mainly used for finishing and for sanding paint, varnish, lacquer, sealers, glass, plastics and stone.
• Zirconia alumina is tough and self-sharpening, but only under machine pressure. With too little pressure it glazes and its life drops, so it suits heavy removal and stainless steel rather than light finish sanding.
• Ceramic aluminium oxide is micro-crystalline and keeps exposing new sharp edges. It was developed for aggressive grinding on metal and gives the most value in removal grits.
• Garnet is a natural grain used for final finish sanding of wood and end grain, though Klingspor notes natural grains are now rarely used.

A frequent misreading is that the hardest grain must be the best. Silicon carbide is the hardest of the four but brittle, and the tougher engineered grains last longer in heavy removal. Colour is no guide either: Klingspor warns that makers dye the size coat and that stearates hide the grain colour, so choose by the grain named on the label.

08Do stearate and open coat matter for grit choice?

Yes, on materials that clog paper. Stearate, usually zinc stearate, is an anti-loading coating, not an abrasive: it stops clogging when sanding finishes, paint, sealer coats, resinous softwoods and soft metals. Open-coat paper leaves space between the grains so dust can clear, which prevents early clogging on wood; closed coat suits harder materials. Grain coverage is graded as closed, semi-open or open.

Most modern abrasives also use resin bonds, which protect the grain from heat and extend its life; older glue bonds soften when hot. When a disc loads up quickly, a stearated or open-coat product in the same grit addresses the clogging directly, without changing the progression.

09Which grain suits metal, paint and plastic?

Metal, paint and plastic each have a different preferred grain, and Klingspor publishes a recommendation for each. Zirconia alumina or aluminium oxide handle carbon and stainless steel; silicon carbide is the usual choice for finishing paint and almost the only choice for plastic and glass. Klingspor recommends zirconia for rough paint stripping and silicon carbide after that, but no manufacturer source in the AccessoryFit fact base gives a full grit sequence for stripping an old finish, so none is given here.

10When does a grit progression fail?

A correct progression still fails when technique, the pad or the disc undermines it. These are the failure points that woodworking guides and abrasive makers describe:

• Too much pressure. Pressing hard slows the pad's rotation and leaves swirls and dished areas. Pressing harder does not make the sander work faster.
• Moving too fast. Fast passes leave uneven loops; aim for about 1 in per second.
• Debris under the disc. A trapped chip makes a high spot, and loose coarse grit scratches the surface on the next grit.
• A disc that will not stay on. A worn or crushed hook face, dust on the pad, poor alignment or worn loop backing are the usual causes. Clean the hook face first, then replace the pad if clean discs still come off.
• Zirconia used at light pressure. The grain glazes instead of self-sharpening.
• A large-orbit sander for the last grit. Popular Woodworking says sanders with small orbits (orbits under 1/8 in) are for finishing, while large orbits leave larger, more visible swirls.

Heavy pressure also crushes the hooks on a hook-and-loop pad and builds heat, so a dull disc should be changed rather than pushed harder.

12Where should you go from here?

For the exact micron figures behind every grade, the sandpaper grit chart lists CAMI and FEPA values from three sources. If you are unsure which discs your sander takes, the accessory finder looks up pad size and hole pattern by model. Pads for corner and detail sanders follow different shapes, covered in the guide to detail sander pad shapes.

Other abrasives, from flap discs to fibre discs, sit in the sanding and grinding accessories section, and more step-by-step guides are collected under technique guides.

13Questions readers ask