Grit measures sandpaper’s coarseness, determined by the size of the abrasive particles on its surface. Fine (100- and 120-grit): The best utility sandpaper. Fine grades smooth scratches left by coarser grades and rough up painted surfaces before accepting new paint. They’re also good for sanding drywall. When you just need some for hand-sanding, or to use with an orbital sander, this is the grade you’ll most likely use.

Super-fine (400-, 500- and 600-grit): Use this for polishing finishes on wood and metal, and to polish bare metal. It comes on waterproof sheets to allow for wet-sanding.

Sanding Blocks

While it’s theoretically possible to manufacture sandpaper grits in tiny progressions, it would be impractical and confuse customers. Consequently, grit numbers increase by standard intervals. The higher the number, the finer the grit. Coarse grits progress from 24 to 30 to 36, while fine ones rise from 600 to 800 to 1,000 and beyond.

It is also the common choice when sanding painted walls, smoothing out plaster and rubbing down filler to blend in with the surface it's on. Extra-coarse (24-, 30- and 36-grit): Generally used for preliminary hardwood floor sanding, this usually comes in belts that fit on a drum sander, or disks that fit an edger. Grits above 320 such as 400 to 600 are typically used to get a really fine finish on wood ready for waxing or polishing. It can also be used to smooth out a top coat and fine wet sanding. Very-fine (150-, 180- and 220-grit): This produces ultra-smooth surfaces on wood. People often use it to scuff-sand lacquer, polyurethane and other finishes before applying another coat.

Sandpaper grit is what makes it abrasive. Manufacturers grade sandpaper based on the size of the grit, and the grade you need depends on the job.

This ranges from120 to 220 grit and is one of the most commonly used grades in home DIY projects. Painting projects often use 120-180 grit for sanding down previously painted surfaces. It gets rid of any minor imperfections and roughs up the surface to provide good adhesion for a new coat of paint. It is also used on bare wood to smooth out ready for the first coat of paint or varnish. The Coated Abrasive Manufacturers Institute (CAMI) and the Federation of European Producers of Abrasives (FEPA) regulate sandpaper grit standards. They refer to the size and number of holes in the screens that filter the abrasive particles. Extra-fine (320- and 360-grit): The first of the micro-abrasives, this is primarily for sanding finishes before polishing. Medium (80-grit): This is often the first grade chosen when going through the grits to prepare wood for finishing. Use it to hand sand, or with a belt or orbital sander. It’s also good for removing rust and corrosion from metal.