Sandpaper is the abrasive that most people buy wrong. Not wildly wrong, but wrong enough to ruin a finishing job or waste a morning of prep work. Understanding grit numbers takes about two minutes, and the payoff is measurable: the right grit removes material faster, protects the workpiece, and produces a better result under paint or varnish.
What does the grit number mean?
The grit number describes the size of the abrasive particles on the paper. Specifically, it refers to how many particles would fit in a one-inch line: a lower number means larger, coarser particles; a higher number means smaller, finer particles.
Think of it in terms of texture you can feel. A 40-grit sheet is like coarse gravel. A 240-grit sheet is like very fine dry sand. A 400-grit sheet is approaching the texture of smooth stone.
Large particles cut and scratch aggressively. Fine particles smooth without removing much material. The progression through grits is about working from aggressive material removal down to fine surface refinement.
The practical grit ranges
40 to 60 grit: heavy removal
This range is for situations where material needs to come off fast. Stripping old paint from a wooden door, removing mill marks from rough-sawn timber, shaping a wooden edge, or flattening a warped board. At this coarseness, the scratches left in the surface are visible to the naked eye, which is exactly why this range is always followed by finer grits before any coating is applied.
Relevant tools: belt sanders, disc sanders, angle grinders with sanding discs.
80 to 120 grit: surface preparation
This is the workhorse range for most trade prep work. After removing old coatings or heavy material with 40 to 60 grit, 80 grit removes the deep scratches from the previous pass and starts producing a surface that is close to ready. Moving up to 100 or 120 brings the surface to a standard that is suitable for priming: no obvious scratches, no mill marks, a consistent scratch pattern that gives primer something to grip.
For new timber that arrived in reasonably good condition, starting at 80 or 100 grit skips the aggressive removal stage and goes straight to surface prep.
Relevant tools: random orbital sanders, half-sheet sanders, belt sanders.
150 to 180 grit: pre-finish sanding
At this stage, the surface should look almost finished, but the scratch pattern from the previous grit is still there under a low-raking light. This range removes that pattern and prepares the surface for the first coat of paint, oil, varnish, or stain.
Joinery trades typically finish pre-coat prep at 150 grit for painted finishes and 180 grit for natural finishes (oils, varnishes, stains) where the scratch pattern can show through a clear coat.
Relevant tools: random orbital sanders with fine pads, hand sanding blocks for detail work.
220 to 240 grit: between-coat sanding
Once the first coat of paint or varnish is dry, sanding back with 220 or 240 grit removes nibs (small dust particles trapped in the wet coating), levels any brush marks, and provides mechanical adhesion for the next coat. The aim is not to remove the coating, only to knock off the imperfections.
For painted surfaces going to a high-gloss finish, between-coat sanding at 240 grit and a light final sand at 320 grit before the final coat produces a result that holds up to close inspection.
Relevant tools: hand sanding block, fine sanding sponge, lightly loaded random orbital.
320 grit and above: final finishing and metal work
Above 320 grit, you are in the territory of surface polishing rather than material removal. On timber, this range achieves a glass-smooth result under clear coatings. On bare metal, it removes corrosion and prepares surfaces for primer or direct painting. On paint, it compresses the final coat surface to a high sheen before cutting compound or wax is applied.
Wet-and-dry (silicon carbide) papers at 400 to 800 grit are used on metal and on automotive paintwork, always with water as a lubricant to prevent clogging and reduce heat.
Backing materials
Paper backing is standard for most hand and machine sanding. It tears if you try to use it wet.
Cloth backing (aluminium oxide on a cotton or polyester cloth) is more durable and is standard on belt sander belts and some orbital sander sheets. It handles heavier workloads without tearing.
Film backing is used on the finest grades and produces the most consistent scratch pattern. It is the backing on quality random orbital sanding discs.
Foam sanding sponges carry abrasive on all four sides and conform to curved surfaces that flat paper cannot follow. They are particularly useful for sanding mouldings, door frames, and decorative profiles.
What grit sandpaper should I use before painting?
For bare timber, work up to 120 or 150 grit before the first coat of primer. For surfaces that are already primed, sand with 220 grit between coats.
What is the correct grit to sand between coats of paint?
220 to 240 grit is standard for between-coat sanding. The aim is to remove nibs and level the surface without cutting through the coating.
Can I skip grits when sanding?
In theory yes, but each grit leaves scratch marks that the next grit is meant to remove. Skipping too many grades means working harder with a finer grit to remove scratches that a mid-range grit would have eliminated quickly.
What grit sandpaper is used for removing paint?
40 to 60 grit on a belt or disc sander for fast removal. If the paint is soft or thin, 80 grit on an orbital sander will strip it more controllably.
Is higher grit sandpaper better?
Higher grit means finer abrasive, which is only "better" for finishing. For material removal, high grit sandpaper is slow and clogs quickly. Always match grit to the task rather than defaulting to the finest available.
What is wet and dry sandpaper used for?
Wet-and-dry (silicon carbide) paper is used on metal and automotive paintwork, always with water. The water prevents the paper clogging and keeps the surface cool. It is not generally used for wood sanding.