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Sandpaper Grit Converterの包括的な教育ガイドを準備中です。ステップバイステップの解説、数式、実例、専門家のヒントをお届けしますので、もうしばらくお待ちください。
The Sandpaper Grit Converter translates between the two major sandpaper grit standards used worldwide: CAMI (Coated Abrasives Manufacturers Institute, the US standard, simple numerical grit like '220 grit') and FEPA (Federation of European Producers of Abrasives, European standard with P-prefix like 'P220'). Despite similar numbering at lower grits, the two systems diverge significantly at finer grits — at CAMI 220 and below, FEPA P-grades are roughly equivalent; above CAMI 220, FEPA particles are smaller and finer than their CAMI counterparts. The calculator outputs equivalents in CAMI, FEPA, and particle size in microns (μm), plus categorizes the grit by use case and suggests the next step in standard sanding progression. The two standards exist because sandpaper manufacturing developed independently on different continents. CAMI was established in 1942 in the US to standardize American abrasives. FEPA was established in 1948 in Europe with slightly different specifications. The differences come from different statistical approaches to particle size distribution — CAMI uses the average particle size to define a grit, while FEPA uses the maximum allowed particle size. This means a FEPA P400 has particles no larger than what CAMI considers average for grit 400 — so FEPA P400 sandpaper is actually somewhat finer than CAMI 400. Understanding grit progression is critical for quality wood and metal work. The fundamental rule: don't skip more than 2× grit at a time. Going from 60 grit (coarse) directly to 220 grit (fine) leaves scratches that the fine paper cannot remove. The proper progression: 60 → 80/100 → 150 → 220 → 320 for typical wood finishing. Each step removes scratches from the previous grit. Skipping causes 'sandpaper memory' where deep scratches from coarse grits show through final finish, especially after staining (which highlights scratches dramatically). This calculator helps you select the right grit, understand cross-system equivalents when shopping, and plan sanding progressions. Enter grit number in CAMI, FEPA, or particle micron. The calculator outputs equivalents in all systems, categorizes the grit (extra-coarse through micro-fine), explains typical uses, and suggests the next step in sanding progression. Use for: woodworking projects, auto body work, jewelry finishing, knife sharpening, and any precision surface preparation.
CAMI grit roughly corresponds to FEPA P-grit at low values; at high grits FEPA represents smaller maximum particle size
- 1Step 1 — Enter Grit Number: Input grit value from sandpaper label or specification. Most common: 80 (coarse), 120 (medium), 220 (fine for wood), 320 (very fine), 600+ (polishing).
- 2Step 2 — Select Source System: Choose CAMI (US grit number like '220'), FEPA (European P-grade like 'P220'), or micron (direct particle size measurement).
- 3Step 3 — Calculator Finds Closest Match: Standard cross-reference table contains 24 standard grit levels from P36 (540 μm) through P3000 (6.5 μm). Calculator finds row matching your input.
- 4Step 4 — Output All System Equivalents: CAMI number, FEPA P-grade, and particle size in microns displayed simultaneously. Use whichever your sandpaper or specification uses.
- 5Step 5 — Review Category and Use Case: Calculator categorizes grit (extra-coarse to micro-fine) and explains typical applications. Helps match grit to project stage.
- 6Step 6 — Plan Next Step in Progression: Calculator suggests the next finer grit to use in proper sanding progression. Following standard progressions prevents 'sandpaper memory' issues.
Sweet spot for stain preparation in wood
CAMI 220 is the most common grit for final pre-stain wood sanding. At this fineness, wood pores remain open enough for stain to absorb evenly while surface is smooth enough to look refined. Going finer (320+) actually closes pores too much for proper stain absorption. Equivalent to European P220 (slightly finer in actual particle size at this grit level).
Most common medium grit for general purpose work
P150 (or CAMI 150) handles general-purpose sanding: removing minor surface imperfections, sanding between primer coats, preparing surfaces for painting, light wood smoothing. Equivalent in both systems at this grit level. About 100 micron particles — coarse enough to remove material, fine enough to leave manageable scratches that finer grits will erase.
Used wet for paint correction and high-gloss finishing
P2000 wet/dry sandpaper is used wet for automotive paint correction (orange peel removal, scratch repair), jewelry final polishing, and lacquer surface refinement. Used with water as lubricant to flush away cut particles. At 10 micron particles, this is approaching polishing compound territory — next step is rubbing compound or polishing wheel.
Use sparingly — removes wood quickly, creates deep scratches
CAMI 60 grit (P60 FEPA) is for aggressive material removal: rough shaping rough lumber, removing thick paint, leveling severely warped surfaces, removing rust from metal. Creates deep scratches that require careful progression through 80 → 100/120 → 150 → 220 to fully erase. Avoid on visible surfaces unless prepared for full grit progression after.
Woodworking — selecting right grit for each project stage from rough to finish-ready
Auto body work — paint correction, scratch repair, and high-gloss finishing
Jewelry making — fine polishing progression from shaping to mirror finish
Knife sharpening — progressive grit sharpening from rough to razor edge
Metalwork — preparing surfaces for paint, polish, or oxide removal
| Project Stage | Start Grit | Progression | Final Grit |
|---|---|---|---|
| Rough lumber prep | 60 | 60 → 80 → 120 → 150 → 220 | 220 (for stain) |
| Smooth wood final | 120 | 120 → 150 → 180 → 220 | 220 (for stain) or 320 (for paint) |
| Painted finish | 150 | 150 → 180 → 220 → 320 | 320 between coats |
| Clear lacquer | 220 | 220 → 320 → 400 → 600 | 600 between coats |
| Auto paint correction | 1500 | 1500 → 2000 → 2500 → 3000 | 3000 + polishing compound |
| Knife sharpening | 400 | 400 → 600 → 1000 → 2000 → 3000 | 3000 + stropping |
What grit should I start with?
Depends on starting condition: rough lumber or paint stripping → 60-80 grit. Mostly smooth lumber with imperfections → 100-120. Already-sanded surface needing refinement → 150-180. Final pre-stain → 220. Between finish coats → 320. Don't skip more than ~2x grit at a time (60 → 80 → 120 → 180 → 220 is correct; 60 → 220 leaves visible scratches).
Can I sand too finely?
For stained wood: yes. Beyond 220 grit, the surface becomes too smooth and pore-closed to absorb stain evenly — patches look blotchy. Stop at 180-220 grit for stained wood. For sealed/painted/clear-coated finishes: go finer (320-600 between coats). For automotive paint correction: 1500-3000 grit is appropriate.
What's the difference between CAMI and FEPA at the same number?
At low grits (≤220): essentially equivalent — CAMI 80 ≈ P80. At high grits (>220): FEPA is finer than equivalent CAMI number. CAMI 400 has particles around 35 μm; FEPA P400 has particles around 35 μm but tighter size distribution (no large outliers), making the actual sanding finer. The difference becomes more pronounced at 600+ grit.
What's wet/dry sandpaper?
Sandpaper that can be used with water as lubricant. Water flushes away cut particles, prevents heat buildup, and produces finer finish than dry sanding at same grit. Standard for fine grits (400+). Common in automotive paint correction, lacquer finishing, jewelry making. Look for 'wet/dry' labeling and silicon carbide (black) abrasive — aluminum oxide (brown/red) is for dry use only.
Why do my finished projects show scratches?
Most likely: skipped grits in progression. Coarse scratches need progressively finer grits to remove. If you went 80 → 220, the 220 cannot remove 80-grit scratches — they remain hidden until finishing (especially staining) makes them visible. Solution: go back, sand at intermediate grit (120 or 150), then up to 220 properly. Always sand with the grain of wood, never across.
プロのヒント
Vacuum or wipe thoroughly between grits — abrasive particles from a coarser grit will undermine your finer sandpaper, leaving scratches that only become visible after finishing. Many failed wood projects trace back to this single mistake. Use compressed air or vacuum with brush attachment between every grit change for best results.
ご存知でしたか？
Sandpaper has been used for over 1,000 years — the earliest sandpaper, dating to 13th century China, was made from shells, sand, and seeds glued to parchment with natural gum. The modern aluminum oxide synthetic abrasive (used in most sandpaper today) was discovered in 1893 by Charles Jacobs, who realized the byproduct of aluminum smelting was harder than natural corundum and could be made in consistent particle sizes. This single discovery enabled the modern precision finishing industry — without consistent abrasives, mass-produced furniture and automotive paint correction wouldn't be possible.