FEPA (P-Grit) vs. CAMI: The Conversion Chart That Explains the Gap
P600 is not 600-grit CAMI. The two scales share numbers at the coarse end and split apart at the fine end — here's the chart, the micron reality, and why it bites you mid-sequence.
Grab a P600 disc and a 600-grit CAMI disc and you do not have the same abrasive. You have two different particle sizes wearing the same number. FEPA's P-scale and the CAMI (US) scale agree at the coarse end and diverge as they get finer — and by the time you're finishing, the gap is wide enough to leave a visible scratch difference through a sequence. This is the reference chart, plus the part the commodity charts skip: why the two standards split, and how micron-graded film and 3M's Trizact scale line up beside them.
They're Not the Same Number
FEPA (Federation of European Producers of Abrasives) grades coated abrasives on the P-scale — a "P" in front of the number, under ISO 6344. CAMI (Coated Abrasives Manufacturers Institute) is the US standard, ANSI B74.18, no prefix. Both count "grit," but they define it differently, and that difference is the whole problem.
Up to about 220 grit, the two scales track each other closely — a P80 and an 80-grit CAMI sit within a few percent on particle size, and you can treat them as interchangeable. Past 220, they separate, and the split grows with every step finer. At the fine end it isn't a rounding error: a P600 averages about 25.8 microns while a CAMI 600 averages about 16 — the P-grade is coarser by more than half again.
Read that direction carefully, because it trips people up: at the same number, the P-grade is the coarser abrasive. To match the fineness of a CAMI 600, you go up to roughly P1200.
The Conversion Chart
Matched by actual particle size, not by number. The coarse grades above the red line are effectively interchangeable; below it — past 220 — the number on the label stops meaning one thing, and the CAMI column shows the grade that matches each P-grade by fineness, not by digits.
| FEPA P-grade | CAMI (by fineness) | Avg particle size | Band |
|---|---|---|---|
| P60 | 60 | 260 µm | Coarse |
| P80 | 80 | 190 µm | Coarse |
| P100 | 100 | 156 µm | Medium |
| P120 | 120 | 125 µm | Medium |
| P150 | 150 | 100 µm | Medium |
| P180 | 180 | 82 µm | Medium |
| P220 | 220 | 68 µm | Fine — last interchangeable |
| P240 | 220–240 | 58.5 µm | Fine |
| P280 | 240 | 52.2 µm | Fine |
| P320 | 280 | 46.2 µm | Fine |
| P360 | 320 | 40.5 µm | Very fine |
| P400 | 320–360 | 35.0 µm | Very fine |
| P500 | 360–400 | 30.2 µm | Very fine |
| P600 | 400 | 25.8 µm | Very fine |
| P800 | 500 | 21.8 µm | Extra fine |
| P1000 | 600 | 18.3 µm | Extra fine |
| P1200 | 800 | 15.3 µm | Extra fine |
| P1500 | 1000 | 12.6 µm | Ultra fine |
| P2000 | 1200 | 10.3 µm | Ultra fine |
| P2500 | 1500 | 8.4 µm | Ultra fine |
| P3000 | 1800–2000 | ~6 µm | Ultra fine |
FEPA-P sizes: ISO 6344 / FEPA 43 d50 values. CAMI matches are closest-fineness, not equal digits.
Why FEPA and CAMI Diverge
Two different definitions of "grit." CAMI specifies an average particle size with a comparatively broad distribution around it. FEPA-P pins each grade to a median (d50) with tight limits on oversize grain — a narrower, more strictly controlled spread. Same nominal idea, different tolerance on how much coarser-than-average grit is allowed in the mix.
That's why P-graded paper tends to cut more uniformly: fewer stray oversize particles digging deeper scratches than the rest of the sheet. It's also why the two scales can't share a number at the fine end — they're fixing different statistics of the same distribution, and the finer you go, the more those definitions pull apart in absolute microns. Here's the same grit number read three ways:
| Grit number | FEPA-P | CAMI | JIS |
|---|---|---|---|
| 120 | 125 µm | 125 µm | 125 µm |
| 180 | 82 µm | 78 µm | 78 µm |
| 240 | 58 µm | 52 µm | 57 µm |
| 320 | 46 µm | 35 µm | 40 µm |
| 400 | 35 µm | 23 µm | 32 µm |
| 600 | 26 µm | 16 µm | 20 µm |
| 800 | 22 µm | 12 µm | 14 µm |
| 1200 | 15 µm | 8 µm | 9 µm |
| 1500 | 13 µm | 6 µm | 8 µm |
| 2000 | 10 µm | 5 µm | 7 µm |
Note: published CAMI micro-grit microns vary by source (coated-abrasive B74.18 vs fused-mineral ANSI). Treat fine CAMI values as nominal.
Same number, three different particle sizes. A disc labeled "1200 grit" with no standard on it could be 15 microns (P) or 8 (CAMI) — close to a 2× difference in scratch depth from one word on a label.
Micron Grades (Film & Lapping) Cross-Reference
Above the P/CAMI range, finishing films and lapping abrasives drop the grit game and label the actual particle size in microns — 30 µm, 15 µm, 9 µm, and down. Cleaner in principle, except the film makers often print a "grit-equivalent" marketing number that matches neither FEPA nor CAMI.
| Micron grade | Film "grit" marking | ≈ FEPA-P | ≈ CAMI |
|---|---|---|---|
| 60 µm | "240" | P240 | 220–240 |
| 40 µm | "320–400" | P360 | 320 |
| 30 µm | "600" | P500 | 360–400 |
| 15 µm | "1200" | P1200 | 800 |
| 9 µm | "2000" | P2000 | 1200 |
| 5 µm | "3000–4000" | ~P5000 | — |
| 3 µm | "4000" | beyond P-scale | — |
| 1 µm | "8000" | beyond P-scale | — |
| 0.5 µm | "10000" | beyond P-scale | — |
A "600" film disc is 30 microns — coarser than both a P600 (25.8) and a CAMI 600 (16). The printed number is marketing; the micron is the truth. On micron-graded product, read the micron and ignore the grit number entirely.
3M Trizact Grade Cross-Reference
Trizact is 3M's structured (micro-replicated) abrasive, graded on its own "A" scale where the number is the nominal mineral size in microns — an A45 is ~45 µm mineral, an A6 is ~6 µm. It shows up constantly in metal finishing and knifemaking, and it doesn't map cleanly to either grit scale, for one specific reason worth understanding.
| Trizact | Nominal mineral | ≈ FEPA-P | ≈ CAMI grit |
|---|---|---|---|
| A500 | 500 µm | ~P50 | 50 |
| A400 | 400 µm | ~P60 | 60 |
| A300 | 300 µm | P80 | 80 |
| A160 | 160 µm | P120 | 120 |
| A130 | 130 µm | P150 | 150 |
| A110 | 110 µm | ~P180 | — |
| A100 | 100 µm | P180 | 180 |
| A90 | 90 µm | P220 | 220 |
| A80 | 80 µm | ~P240 | 240 |
| A65 | 65 µm | P280 | 240–280 |
| A45 | 45 µm | P400 | 320–360 |
| A35 | 35 µm | ~P500 | 360–400 |
| A30 | 30 µm | P600 | 400 |
| A20 | 20 µm | ~P1000 | 600 |
| A16 | 16 µm | P1200 | 800 |
| A10 | 10 µm | P1500 | 1000 |
| A6 | 6 µm | P2500 | 1500–2000 |
| A5 | 5 µm | P3000 | ~2500 |
| A3 | 3 µm | beyond P-scale | — |
Trizact equivalents per 3M product application guide. "A" number = nominal mineral micron.
Note the mismatch built into that table: an A45 is nominally 45 microns but finishes like a P400 (35 µm), and an A6 (6 µm) finishes like a P2500 (8.4 µm). The A-number runs coarser than the finish it actually leaves, because Trizact's uniform pyramids present abrasive continuously and cut finer than a pile of loose grain of the same size would. Read Trizact by its published grit-equivalent — never by assuming its micron number lines up with a FEPA or CAMI micron.
Where It Bites You: Mixed-Standard Grit Stacks
Here's the real-world failure. You build a finish sequence — say 320 → 400 → 600 → 800 — pulling discs from whatever's in the drawer or cheapest that week. Half are P-graded imports, half are CAMI. On paper it's a clean progression. In the metal it isn't: your "400" steps are different sizes depending on the standard, and a later "600" from one standard can actually be coarser than an earlier "400" from the other. The result is scratches that won't refine out, because a step you thought was finer is putting deeper marks back in.
The fix is discipline, not a better chart. Pick one standard and stay on it through a whole sequence. If you have to mix, convert by micron — not by the printed number — and confirm each step is actually finer than the last. When you're specifying a finish to an Ra target, the standard your grit is graded in is part of the spec, not a footnote. And when you're picking start and finish grit for a given material, work it as a micron progression — the grit selection guide walks the material-by-material version.
FAQ
Is P600 the same as 600 grit?
No. P600 (FEPA) averages about 25.8 microns; CAMI 600 averages about 16. The P-grade is noticeably coarser. To match a CAMI 600's fineness on the P-scale, you're closer to P1200.
Which is finer at the same number, FEPA or CAMI?
CAMI, at the fine end. Past roughly 220 grit, a CAMI number is a smaller particle than the same P-number. Below 220, they're effectively the same.
Why do the two scales agree on coarse grit but not fine?
The definitions diverge as particle size shrinks. FEPA-P holds a tight median with limited oversize grain; CAMI allows a broader distribution. At coarse sizes the difference is negligible; at fine sizes it compounds into a real micron gap.
How does 3M Trizact compare?
Trizact's "A" number is the nominal mineral size in microns, but it finishes finer than that number suggests — an A45 behaves like roughly P400. Use its published grit-equivalent rather than reading the A-number as a FEPA or CAMI micron.
What about micron-graded film discs?
Those are labeled in actual microns and are the most precise. Ignore any "grit" number printed alongside — a "600" film is 30 microns, which matches neither P600 nor CAMI 600. Read the micron.
