100 vs 120 Grit Sandpaper: Which One Should You Use?

Quick answer

Use 100 grit when the surface still needs faster leveling or when a previous coarse step has left scratches that 120 grit would remove too slowly. Use 120 grit when the surface is already reasonably even and you want a slightly finer, easier-to-refine scratch pattern. The difference is modest, so you do not always need both. A test patch should decide.

The important distinction is not that one grit is “for wood” and the other is not. Both can be useful on compatible wood, coatings, filler, or metal-preparation jobs. The correct choice depends on the defect, the substrate, the abrasive system, and what must happen next.

100 grit and 120 grit at a glance

Grit numbers are nominal classifications, not a promise that every abrasive product cuts identically. Mineral, backing, coating density, pressure, tool speed, and wear can change the result. Compare the actual sheets on a hidden test area whenever the finish matters.

Choose 100 grit when the surface still needs correction

100 grit is the better choice when efficiency matters more than immediate refinement. It can bridge from 80 grit, reduce shallow ridges, soften an old coating edge, or level rough stock before a finer pass. It is also useful when 120 grit skates over the surface without removing the remaining pattern at a reasonable rate.

Do not treat faster cutting as permission to press harder. Use a firm, appropriate backing on flat work, make overlapping passes, and keep the tool or block moving. Clean the surface and inspect frequently. Stop when the remaining marks are uniform; staying with 100 grit after its job is complete only deepens the pattern that the next grit must remove.

For more detail on its role and limits, see the 100 grit sandpaper guide.

Choose 120 grit when the surface is already close

120 grit is usually the more conservative starting point when the surface is flat and the goal is to refine rather than reshape it. It can smooth a 100-grit pattern, prepare many bare-wood surfaces for later sanding, and make a controlled transition toward 150, 180, or 220 grit.

Choose 120 first when a test patch removes the defect without excessive time or pressure. The shallower pattern is normally easier to refine, which can reduce the total work even though each pass cuts more slowly. If 120 grit is barely changing the defect, however, forcing it is not safer; it can encourage uneven pressure and rounded edges.

The 120 grit sandpaper guide explains common sequencing mistakes and useful inspection checks.

Do you need to use both?

Not always. Moving from 100 to 120 is a small step. Whether it earns a place in the sequence depends on the surface and the finish that follows.

Use both when the 100-grit pattern remains obvious under raking light, the next planned grit struggles to erase it, or the finish is likely to reveal directional scratches. Skip one when a test panel proves that the next grit removes the prior pattern evenly without excessive time, heat, pressure, or sheet use.

A practical test is simple:

1. Sand one small area with 100 grit until the defect is replaced by a uniform pattern.
2. Refine half of that area with 120 grit and the other half with the next planned grit.
3. Clean both halves completely.
4. Inspect under low-angle light and by touch.
5. Keep the shorter sequence only if the result is equally uniform.

This test is more reliable than a universal grit-jump rule because the coating, wood species, tool, and abrasive all influence the outcome.

A controlled sanding sequence

Start by cleaning the work so loose grit cannot make new scratches. Mark the test area lightly with pencil where that is safe for the substrate. Sand with consistent pressure and overlap, then vacuum or wipe the residue away before inspection.

If 100 grit is required, use it only until the original defect and any coarser scratches are gone. Change direction or use a pencil map at the next step so the new 120-grit pattern is easier to distinguish. Do not advance while isolated 100-grit lines remain; fine sanding can soften their edges without actually removing them.

Edges, corners, veneer, and thin coatings deserve extra caution. Back the sheet appropriately, reduce pressure near vulnerable geometry, and follow the material or coating manufacturer's instructions when a specified preparation profile is required.

Product options from the catalog

For a side-by-side sheet comparison, eQualle lists 100 grit waterproof sandpaper in a 25-sheet pack and 120 grit waterproof sandpaper in a 25-sheet pack. The same catalog-backed items are available through Amazon as 100 grit sheets and 120 grit sheets.

You can also browse the 100 grit collection and 120 grit collection for other listed quantities. Pack size is a purchasing choice, not evidence that a project requires a specific number of sheets.

Related video

This short eQualle video shows a 100-grit refinishing use case. Use it as a visual reference for the coarser side of the comparison, then confirm the starting grit with a test patch on your material.

FAQ

Is 100 grit much rougher than 120 grit?

100 grit is coarser and normally cuts faster, but the two grades are neighbors rather than opposites. Product construction and sanding method can make the practical difference feel larger or smaller.

Can I go from 100 grit straight to 150 grit?

Often, but only a test area can confirm it. If 150 grit removes the complete 100-grit pattern efficiently and evenly, the 120-grit step may not add value.

Is 120 grit a finishing grit?

Sometimes it is the last bare-wood step specified for a particular finish, but it is not universally a finishing grit. Follow the finish manufacturer's guidance and test for scratch visibility and absorption.

Which grit should I use before paint?

That depends on whether you are leveling bare material, sanding primer, or scuffing an intact coating. Use the paint or primer maker's specified preparation range instead of choosing solely between 100 and 120.