Sanding grit progression is the systematic sequence of moving from coarser to finer abrasive grits to achieve a smooth surface. Proper progression removes scratches left by the previous grit while minimizing effort. A good rule of thumb: never skip more than 50% of the previous grit number. For example, after 80 grit, move to 120 (50% jump), not directly to 220 (175% jump), which would leave deep scratches visible under finish.

For most woodworking projects, 3 to 5 grit stages are recommended. A typical progression for hardwood is 80 → 120 → 180 → 220. For fine finishing, extend to 320 or 400 grit. Each stage should use a grit approximately 30–50% higher than the previous one. Jumping too far creates scratches that are difficult to remove; too many steps wastes time and sandpaper.

The most common woodworking progression is 80 → 120 → 180 → 220 grit. This works well for hardwoods like oak and maple. For softwoods (pine, cedar), start at 100 or 120 grit since they scratch more easily. For exotic hardwoods or when using water-based finishes, extend to 320 or 400 grit. Always end-grain sand to one grit finer than face grain to ensure even stain absorption.

Skipping one grit in a sequence is sometimes acceptable (e.g., 80 → 120 → 220), but skipping two or more is risky. The deeper scratches from the coarser grit may not be fully removed, becoming visible only after applying stain or finish. If you must reduce steps, spend extra time with the intermediate grit to ensure all previous scratches are eliminated before moving on.

Between coats of polyurethane, varnish, or lacquer, use 320 to 600 grit sandpaper. The goal is not to remove material but to scuff the surface for mechanical adhesion of the next coat. Use very light pressure — just enough to dull the shine. For water-based finishes, 400 grit is ideal. For final coats, use 600+ grit or ultra-fine Scotch-Brite pads (equivalent to 800–1000 grit).

Softwoods (pine, cedar, fir) scratch easily and benefit from closer grit progression — use smaller jumps (≤40%). Hardwoods (oak, maple, walnut) tolerate moderate jumps (≤50%). Exotic hardwoods (rosewood, ebony, purpleheart) are dense and show fine scratches, requiring tighter progression (≤30%). Plywood and veneer require extra caution — the thin surface layer can be sanded through, so start finer (150+) and progress carefully with minimal pressure.

Grit numbers follow the FEPA (European) or CAMI (US) standards. Approximate micron equivalents: 80 grit ≈ 200µm, 120 grit ≈ 125µm, 180 grit ≈ 78µm, 220 grit ≈ 65µm, 320 grit ≈ 46µm, 400 grit ≈ 35µm, 600 grit ≈ 26µm, 800 grit ≈ 21µm, 1000 grit ≈ 18µm, 1500 grit ≈ 10µm, 2000 grit ≈ 8µm. Micron size represents the average particle diameter — lower numbers mean coarser abrasives.

You're ready to move to the next grit when: (1) The surface feels uniformly smooth under your hand across the entire piece. (2) There are no visible scratch patterns from the previous grit — use raking light at a low angle to check. (3) The sanding dust is fine and consistent. (4) On end grain, the surface no longer feels fuzzy. A common mistake is rushing — each grit typically needs 1–3 minutes per square foot for proper scratch removal.