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About this tool
Builds the grit sequence from stripping to final finish for your material, with FEPA to CAMI conversion, sheet counts and sanding time.
Generates the grit progression for a sanding job from the state of the surface to the finish going on top of it. The sequence is built from abrasive particle size rather than habit: each step drops the average particle diameter by no more than 1.65 times and skips at most one grade, which is what produces the familiar 80-120-180-220 run. It also converts between the FEPA (P-prefixed) and CAMI grit standards, which agree up to about 220 and diverge badly after it.
Open Sandpaper Grit Selector on AltFTool — it loads instantly in your browser.
Add your input to the workspace.
Adjust the options until the result looks right.
Copy or download the output and put it to work.
Sequences come from particle sizes, so they hold for any start and stop point.
The finish decides the final grit — paint needs a key, oil hides nothing.
Veneer, clear coat and thin ply will not be sent a grit that cuts through them.
P150 on softwood and P180 on hardwood. Going finer burnishes the surface and closes the pores, which makes the stain sit on top rather than soaking in, and any burnished patch shows as a pale blotch. For a clear film finish like polyurethane, P220 is the sensible stopping point.
One grade at most, and only where the particle sizes are close. The job of each grit is to remove the scratch pattern of the previous one, so if the jump is too large the finer paper only polishes the ridges and leaves the valleys. As a rule the particle size should not drop by more than about 1.65 times between steps.
No. CAMI 400 has an average particle size around 23.6 microns, while P400 is about 35 microns — CAMI 400 is closer to P800. The two standards track each other up to roughly 220 and separate above it, so a fine-grit sheet from a different market can behave quite differently from the number on the back.
Start at P60 for stripping paint or varnish, and P40 only for levelling genuine damage. Coarser than that gouges the substrate, and on anything painted before the late 1970s do not dry-sand at all — the paint may contain lead, which needs chemical stripping or professional removal instead.