How to Calculate Sandpaper Grit Converter
What is Sandpaper Grit Converter?
The Sandpaper Grit Converter translates between the two major sandpaper grit standards: CAMI (Coated Abrasives Manufacturers Institute, US standard, simple numerical grit like 220) and FEPA (Federation of European Producers of Abrasives, European standard with P-prefix like P220). Despite similar numbering, the two systems use different particle size measurements — at low grits (below 220) they're roughly equivalent; at high grits (above 220) FEPA particles are smaller and finer.
Formula
- G
- Grit Number (CAMI or P) — Industry standard grit measurement
- μm
- Particle Size (microns) — Actual abrasive particle diameter
Step-by-Step Guide
- 1Enter grit number in CAMI, FEPA, or particle size (micron)
- 2Calculator finds closest match in standard reference table
- 3Outputs CAMI number, FEPA P-grade, and particle size in microns
- 4Categorizes by use case: extra-coarse, coarse, medium, fine, very fine, extra fine, super fine, micro fine
- 5Suggests next step in sanding progression
Worked Examples
Common Mistakes to Avoid
- ✕Assuming CAMI 320 equals FEPA P320 — at higher grits they diverge significantly
- ✕Skipping grits in sanding progression — should go up no more than 2x grit (60→80→120 not 60→200)
- ✕Using too fine grit on rough wood — wastes paper and time without removing material
- ✕Not cleaning surface between grits — coarser dust degrades finer grit performance
Frequently Asked Questions
What grit should I start with?
Depends on starting condition: rough lumber → 60-80 grit. Smooth lumber → 100-120. Already-sanded → 150-180. Final before staining → 220. Between coats → 320. Don't skip more than ~2x grit at a time.
Can I sand too finely?
For staining wood, yes — beyond 220 grit, the surface becomes too smooth to absorb stain evenly. Stop at 180-220 grit for stained wood. For sealed/painted/clear-coated finishes, go finer (320-600 between coats).
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