Sandpaper Grit Guide: Choosing the Right Abrasive for Sanding Wood, Metal & Finishing

Understanding Grit Numbers

Sandpaper grit numbers tell you the size of the abrasive particles bonded to the backing. Lower numbers mean larger, more aggressive particles; higher numbers mean finer particles for smoother finishes. The number roughly corresponds to the number of particles that would fit across one linear inch: 80-grit particles are about 0.007 inches (180 microns) in diameter, while 220-grit particles are about 0.003 inches (68 microns). CAMI (Coated Abrasives Manufacturers Institute) is the grading standard used in North America; FEPA (Federation of European Producers of Abrasives) uses a P-prefix (P80, P220). The two systems are close but not identical at higher grits — FEPA P400 is finer than CAMI 400.

Grit Ranges and Uses

Coarse (40-60 grit): aggressive material removal. Use for shaping, leveling, stripping old paint or finish, removing deep scratches, and initial sanding of very rough lumber. Removes material fast but leaves deep scratches that require significant work to remove. Medium (80-120 grit): the workhorse range for woodworking. 80 grit removes mill marks and levels joints. 100 grit is common for initial sanding of pre-surfaced lumber. 120 grit is the standard starting point for most projects and the minimum for paint preparation.

Fine (150-180 grit): smoothing and finish preparation. 150 grit is the standard pre-stain sanding for most projects. 180 grit produces a smooth surface suitable for most stains and clear finishes. This is where most woodworkers stop sanding bare wood before applying finish. Very fine (220-320 grit): final preparation and between-coat sanding. 220 grit is the gold standard for final sanding before finish application and for scuff-sanding between coats of polyurethane, lacquer, or varnish. 320 grit is used between coats of lacquer and for fine finishing. Ultra-fine (400-2000+ grit): wet sanding, polishing, and rubbing out finishes. 400 grit wet-sands between coats of automotive or high-gloss finishes. 600-2000 grit progressively polishes cured finish coats to a mirror-like gloss.

Abrasive Types

Aluminum oxide (brown/tan): the most common and versatile abrasive for wood. Durable, self-sharpening (particles fracture to expose fresh cutting edges), and affordable. Works well on all wood species and for general-purpose sanding. Garnet (reddish-brown): natural mineral that wears faster than aluminum oxide but produces a smoother scratch pattern at equivalent grits. Traditional choice for final hand sanding before finishing, especially for staining, because it burnishes the wood less than harder abrasives. Silicon carbide (black/dark gray): harder and sharper than aluminum oxide. The standard for wet sanding, sanding between finish coats, and sanding metal. Zirconia alumina (blue/purple): extremely durable for heavy stock removal, especially on metal. Used in belt sander belts for aggressive leveling. Ceramic (red/dark red): the most durable and aggressive abrasive. Used in premium sanding belts and discs for maximum material removal and longest life. Costs more but lasts 2-5 times longer than aluminum oxide.

Sanding Sequence for Wood

1. The key principle: each grit removes the scratches left by the previous grit. You can't skip more than one grit step — jumping from 80 to 220 leaves visible 80-grit scratches under the finish. The standard wood sanding sequence: 80 (if starting rough) to 120 to 150 to 180 or
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4. For paint: 80 to 120 to 150 is sufficient. For clear finish (polyurethane, lacquer, oil): go to 180 or
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7. For staining: many finishers stop at 150 because oversanding (especially past 220) can close the wood pores and create blotchy stain absorption, particularly in softwoods like pine and cherry.

Power Sander Tips

Random orbital sanders (the most common power sander for woodworking) use 5-inch hook-and-loop discs. Sand with even pressure, let the sander do the work, and move slowly in overlapping passes. Don't press hard — excess pressure slows the orbital action and creates swirl marks. Keep the sander flat, not tilted. For belt sanders, sand with the grain direction. Belt sanders remove material aggressively — use them for leveling and shaping, then switch to a random orbital for final smoothing. Always finish by hand-sanding lightly with the grain using the same final grit to remove any cross-grain swirl marks left by the orbital sander.