Sanding past 220 on anything to be stained Using an orbital sander for the last pass on a piece to be stained — swirl marks show as dark rings Leaving dust in the grain; it becomes part of the finish

Which sandpaper grit for bare wood before finishing?

80 to 120 to 150 on softwood, finishing at 180 or 220 on hardwood — and stop there, because over-sanding ruins stain.

Sanding is a sequence, not a grit: each grade exists to remove the scratches left by the one before, so skipping from 80 straight to 180 leaves deep marks that only appear once a finish goes on and reflects light. The counterintuitive part is the upper limit. Sanding past about 220 closes the wood's surface, and a burnished surface accepts less stain — which is what produces blotchy, uneven colour on softwoods and on cherry and maple. Water-based finishes raise the grain, since water swells the cut fibre ends, so wiping the surface with a damp cloth, letting it dry and cutting back lightly gets that out of the way before the first coat.

The options, ranked

Ranked best-first for the stated job. The third column is why the others exist.
Option	Good at	Bad at
80 grit	Levels machine marks, glue residue and mild damage quickly.	Leaves scratches that show through a clear finish if you stop here.
120-150 grit	The workhorse for softwood being painted; removes the previous grit's scratches and leaves a good key.	Not fine enough under a clear finish on hardwood.
180-220 grit	The right stopping point for hardwood under an oil, varnish or lacquer.	Going beyond it burnishes the surface, and stain then goes on patchy.
Sanding sealer or a raised-grain pass	Wetting the wood, letting it dry and cutting back with 220 stops the first coat raising the fibres.	An extra step, and it must be done before staining, not after.

Technique that changes the outcome

Work up through the grits without skipping more than one step
Sand along the grain; cross-grain scratches show under any clear finish
Wipe with white spirit or water to reveal scratches before finishing
Raise the grain deliberately with a damp cloth before a water-based finish, then cut back at 220

What goes wrong

Sanding past 220 on anything to be stained
Using an orbital sander for the last pass on a piece to be stained — swirl marks show as dark rings
Leaving dust in the grain; it becomes part of the finish

Compiled practical guidance rather than a published standard. Product formulations vary by brand and market, so read the label — and where the work is structural, electrical or gas, the regulations that apply where you are govern rather than anything here.

For	Use
Stripping paint	40 to 80 grit open-coat aluminium oxide or ceramic — but test for lead paint before sanding anything painted before the 1990s.
Rusty metal	60 to 80 grit to strip scale, 120 to 180 to blend — then prime the same day, because bare steel flash rusts within hours.
Between coats	220 to 320 grit with almost no pressure — you are knocking off dust nibs, not removing the coat.
Plasterboard filler	120 to 150 grit to level joint compound and 220 for the final pass, ideally on a mesh with a vacuum attached.
Plastic	Start at 320-600 wet for scratches, work up to 2000, then finish with a plastic polish — and keep it cool.
Car body filler	80 grit to shape, 180 to refine, 320 before primer and 400-600 on the primer before paint.
Final finish	400 to 600 dry, or 800 to 2000 wet on a fully cured film, followed by a polishing compound.
Wet sanding	Silicon carbide wet-or-dry paper, water with a drop of detergent, a rigid block, and 800 grit upwards.

Common questions

Which sandpaper grit for bare wood before finishing?: 80 to 120 to 150 on softwood, finishing at 180 or 220 on hardwood — and stop there, because over-sanding ruins stain.
What should I avoid?: Sanding past 220 on anything to be stained Using an orbital sander for the last pass on a piece to be stained — swirl marks show as dark rings Leaving dust in the grain; it becomes part of the finish

Which sandpaper grit removes paint? 40 to 80 grit open-coat aluminium oxide or ceramic — but test for lead paint before sanding anything painted before the 1990s.
Which sandpaper grit removes rust? 60 to 80 grit to strip scale, 120 to 180 to blend — then prime the same day, because bare steel flash rusts within hours.
Which sandpaper grit between coats of paint or varnish? 220 to 320 grit with almost no pressure — you are knocking off dust nibs, not removing the coat.
Which sandpaper grit for plasterboard and filler? 120 to 150 grit to level joint compound and 220 for the final pass, ideally on a mesh with a vacuum attached.
Which sandpaper grit for plastic? Start at 320-600 wet for scratches, work up to 2000, then finish with a plastic polish — and keep it cool.
Which sandpaper grit for car body filler? 80 grit to shape, 180 to refine, 320 before primer and 400-600 on the primer before paint.
Which sandpaper grit for a final finish? 400 to 600 dry, or 800 to 2000 wet on a fully cured film, followed by a polishing compound.
Which sandpaper should I use for wet sanding? Silicon carbide wet-or-dry paper, water with a drop of detergent, a rigid block, and 800 grit upwards.
Which paint should I use on bare wood? Paint

Sources

Typical range compiled from manufacturer specifications — At One Place

How these figures are compiled and checked