Sandpaper Grit Numbers Explained

Sandpaper grit numbers tell you how coarse or fine the abrasive particles are, which directly determines how much material the paper removes and how smooth the finish will be. Lower numbers (like 40 or 60) are coarse and cut fast, while higher numbers (like 220 or 400) are fine and produce a smoother surface.

How Grit Numbers Work

The number on sandpaper refers to the size of the abrasive grains bonded to the backing. It is based on how many openings per inch a sieve has when the grains are sorted. A grit of 60 means the particles passed through a screen with 60 openings per inch; a grit of 120 passed through 120 openings per inch. So higher numbers mean smaller particles, which produce finer scratches.

Particle size is roughly inversely proportional to the grit number. A simple approximation is:

Particle diameter (microns) ≈ 15,000 ÷ grit number

For example, 60-grit particles are about 250 microns (0.25 mm), while 400-grit particles are about 38 microns. This is only an approximation because different standards (CAMI vs. FEPA) and different abrasive materials (aluminum oxide, silicon carbide, etc.) have slightly different sizes for the same number.

Grit Number Ranges and Their Uses

• Very Coarse (24–40 grit): Heavy stock removal, stripping paint, shaping wood, removing rust. Leaves deep scratches.
• Coarse (50–80 grit): Initial sanding of rough lumber, removing old finish, smoothing edges after cutting. Still leaves visible scratches.
• Medium (100–150 grit): General-purpose sanding, preparing bare wood for finishing, removing small imperfections. Most common range for DIY projects.
• Fine (180–240 grit): Final sanding before applying primer or paint, sanding between coats, smoothing bare wood for a natural finish.
• Very Fine (320–400 grit): Sanding between finish coats, polishing metal, wet-sanding automotive paint. Produces a satin or semi-gloss sheen.
• Extra Fine (600–1200+ grit): Wet-sanding clear coats, polishing plastics, achieving a high-gloss mirror finish. Often used with water as a lubricant.

How to Choose the Right Grit

Start with a grit that matches the condition of your surface. If you have deep scratches or old paint, begin coarse (60–80) and work your way up. If the surface is already smooth, start at 120–150. Always progress through grits in steps – don’t jump from 80 to 220. A typical sequence is 80 → 120 → 180 → 220. Skipping grits leaves deeper scratches that the finer grit can’t remove.

• Bare wood: Start at 80–100, finish at 180–220.
• Paint prep: Start at 120–150, finish at 220.
• Between coats: Use 320–400, lightly.
• Metal: Start at 120–180, finish at 400+ for polishing.
• Drywall: Use 120–150 for joint compound, 220 for final.

Common Mistakes and Misconceptions

“Higher grit is always better.” Not true – using too fine a grit on rough wood wastes time and clogs the paper. Coarse grits are needed to remove material efficiently.

“You can skip grits.” Skipping from 80 to 220 leaves 80-grit scratches that 220 can’t remove. You’ll see them after finishing. Always step through grits.

“Sandpaper lasts forever.” Abrasive grains dull and clog. When the paper stops cutting or feels smooth, replace it. Clogged paper can be cleaned with a rubber eraser block, but worn paper is done.

“Wet and dry are the same.” Wet-or-dry sandpaper is made with a waterproof backing and resin bond, so it can be used with water. Regular sandpaper falls apart when wet.

Grit Standards: CAMI vs. FEPA

Two main standards are used worldwide. The Coated Abrasives Manufacturers Institute (CAMI) is common in North America, and the Federation of European Producers of Abrasives (FEPA) is used in Europe and most of the world. FEPA numbers are often followed by a “P” (e.g., P120). The scales are similar but not identical. For example, CAMI 120 is roughly equivalent to FEPA P120, but at higher grits they diverge: CAMI 400 is about FEPA P600. For most DIY work, the difference is negligible, but for precision work, check which standard your paper uses.

Safety and Best Practices

Always wear a dust mask when sanding – fine dust is harmful to lungs. Use eye protection, especially when sanding overhead. Work in a well-ventilated area. When sanding metal, use a respirator rated for metal dust. Keep your sandpaper flat and use even pressure – let the paper do the work. Move in the direction of the wood grain for final passes. For curved surfaces, use a flexible backing pad or sand by hand.

Frequently Asked Questions

What does “grit” actually mean?

Grit is the size of the abrasive particles. It’s determined by sifting the grains through a screen with a specific number of openings per inch. A 100-grit paper uses grains that passed through a 100-mesh screen.

Can I use water with any sandpaper?

No. Only “wet-or-dry” sandpaper (usually silicon carbide) is waterproof. Regular sandpaper has a paper backing that falls apart when wet. Wet sanding reduces clogging and produces a finer finish, especially on paint and clear coats.

What’s the difference between aluminum oxide and silicon carbide?

Aluminum oxide is tough and long-lasting, ideal for wood and metal. Silicon carbide is sharper and harder, but breaks down faster; it’s used for wet sanding, glass, and plastics. For most woodworking, aluminum oxide is the better choice.

How do I know when to move to the next grit?

When the scratches from the current grit are uniform and you can’t see any deeper scratches from the previous grit, it’s time to move up. Run your fingers over the surface – it should feel consistently smooth, with no visible swirls or gouges.

Is higher grit always smoother?

Yes, higher grit leaves finer scratches, so the surface feels smoother. But if you skip grits, the deeper scratches from the coarse grit remain and will show through the finish. Always work through the grits sequentially.

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in grit | Grit number | - | 120 | 0
out avg_particle | Approx. particle size | microns | 15000 / grit | 0