Sandpaper Grit Chart

How to choose the first grit

The first grit should remove the defect with the least unnecessary damage to the surrounding surface. Decide whether you are removing a thick layer, flattening tool marks, refining an already flat surface, or abrading an existing coating for its next coat. Those tasks need different scratch depths. A new, planed board does not automatically need the same coarse paper as a painted, weathered board.

Test a small area with a moderate grade. If it cuts too slowly despite fresh paper and suitable pressure, move coarser. If it leaves unnecessarily deep marks or quickly changes the shape, move finer. For bare wood, Norton’s guide places heavy removal near 40–60 grit and general smoothing near 80–120. These are starting ranges, not instructions to use every grit on every project.

Thin veneer, edges and profiles need extra control because a local mistake can remove the decorative surface. Keep the abrasive supported and inspect the surface between stages. A grit chart cannot estimate the remaining veneer or coating thickness.

A sanding sequence that removes the previous scratches

A finer grade should remove the scratches left by the preceding grade before you move on. Skipping directly from very coarse paper to a very fine paper often spends time polishing the high spots while the deeper scratches remain. Clean the surface between grades so stray coarse particles do not continue scratching it.

The bare-wood sequence follows Festool’s planer-mark example; the intercoat range follows Mirka’s intermediate-sanding range; primer grades follow Norton’s automotive application guide. They describe distinct operations. Do not combine the entire table into one universal sanding recipe.

For drywall, USG’s product-specific guidance distinguishes paper from mesh. For metal, Norton’s Metal AO cloth-sheet specification gives the stated grades. These are separate material-specific examples; a wood sequence should not automatically be applied to drywall or metal.

FEPA P, CAMI and micron labels: what changes?

FEPA P identifies coated-abrasive grading. FEPA uses different designations for bonded abrasives and superabrasives, so a grinding-wheel F grade or a diamond grade should not be read as a sandpaper P grade. FEPA’s standards explanation also makes clear that particle distributions matter: a grade is not a bag of particles all having one exact diameter.

CAMI / U.S. is a separate comparison scale. A package without a P prefix does not always prove that its grade is CAMI; verify the product label or manufacturer’s technical information. Manufacturer naming can also distinguish a commercial grade from a formal grading standard.

Microns give a physical size unit. The values here let you recognize large differences and find a nearby grade, but matching an average alone cannot guarantee the same surface finish. Mineral, coating density, backing, sanding pad, pressure and machine motion also affect the scratch pattern. Use one coherent abrasive and coating process when the finish must be repeatable.

Worked example: replacing a “400 grit” sheet

Suppose a process specifically calls for CAMI 400. This chart gives approximately 23.6 µm. A sheet marked P400 is approximately 35 µm, so it has a coarser characteristic grain size despite the identical number. The P grade nearest the CAMI 400 average in this dataset is P800 at about 21.8 µm.

The arithmetic is useful: (35 − 23.6) ÷ 23.6 ≈ 48%, so the P400 comparison size is about 48% larger. That does not predict a scratch exactly 48% deeper, a fixed removal-rate increase, or an acceptable process substitution. Confirm the replacement with the abrasive and coating supplier and make a test panel. The source values come from CAFA’s comparison chart.

If the original instruction merely says “400” without identifying the product or standard, resolve that ambiguity before selecting the replacement. A precise-looking conversion cannot repair an unspecified starting grade.

Why finer paper does not always give a better finish

The goal is a surface that accepts the next operation, not the highest possible grit number. Very fine sanding before a penetrating stain can change absorption and appearance. Sanding an intermediate coating too aggressively can cut through it, while using a process that is too fine for the next coating can fail to create the intended surface preparation. Follow the finish maker’s directions and compare a finished sample, not just the feel of bare wood.

Dust safety: Use suitable dust extraction and respiratory protection, especially for wood dust and drywall dust. Before disturbing old paint, check applicable lead-paint precautions. Do not dry sand asbestos-containing materials.

Wet sanding is also a separate process choice. Use it only with a wet-rated abrasive and a compatible, sufficiently cured surface. An abrasive grade does not say whether its backing tolerates water or whether the substrate should be wetted.

Common causes of disappointing results are skipping scratch-removal steps, reusing loaded paper, pressing harder to compensate for a worn abrasive, leaving dust on the surface, and treating a polishing grade as a bare-wood finishing requirement. Norton’s bare-wood guidance emphasizes matching the final sanding stage to the wood and finish rather than assuming that ever-finer paper is always preferable.

Sandpaper Grit Chart FAQs

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