FEPA vs CAMI Grit Scales: Why \"400 Grit\" Isn't Always 400

Quick Answer

FEPA P and ANSI/CAMI are two different grit-grading standards. They agree at coarse grits (about P220 and below) but diverge in the fine range, where FEPA-P numbers run higher than CAMI for the same grain. A FEPA P400 disc (~35 µm) is coarser than a CAMI 400 disc (~14–23 µm). Always confirm which scale graded a product first.

Two scales, one number line they were never meant to share

Pick up a sanding belt marked "400 grit" and you would assume 400 is 400 everywhere. It is not. A grit number is only meaningful next to the standard that defined it, and the abrasives world runs two main coated-abrasive scales side by side.

FEPA — the Federation of European Producers of Abrasives — maintains the system used across most of the world outside North America. Its coated-abrasive grades carry a "P" prefix (P120, P400) under standards such as FEPA 43-1:2006 (macrogrits) and FEPA 43-2:2006 (microgrits), published by FEPA. A higher number always means a finer grain (FEPA; Washington Mills, 2026).

ANSI/CAMI — the North American scale run by the Coated Abrasives Manufacturers Institute — is what a US or Canadian buyer meets by default when a disc is sold simply as "120 grit" with no prefix. It is codified in ANSI B74.18, the North American standard for grading abrasive grain on coated material (FEPA / ANSI conversion references, 2026).

These are independent grading systems. They map only roughly onto each other, and that mapping is published as a conversion chart, not a formula. For the underlying grain-selection logic by job, see our abrasive grit chart for metalworkers.

Where the scales agree — and where they split

The good news: at coarse grits the two scales are close to numerically interchangeable. At roughly P220 / CAMI 220 and below, a P-number and a plain CAMI number point to the same physical grain. CAMI 60 sits at about 268 µm, FEPA P60 at about 269 µm — effectively identical (FEPA / CAMI charts, 2026).

The bad news: above that point they diverge progressively through the fine range, with FEPA-P numbers running higher than CAMI for the same particle size. By the time you reach the polishing grits, the gap is roughly a factor of two on the printed number.

Fine grit	FEPA P	≈ CAMI	What this means
medium-fine	P400 (~35 µm)	CAMI 400 (~14–23 µm)	Not equal — FEPA P400 is the coarser one
fine	P600 (~26 µm)	≈ CAMI 400	the numbers start to cross over
very fine	P1200 (~15 µm)	≈ CAMI 600	CAMI now lags well behind
ultra-fine	P2500 (~8 µm)	≈ CAMI 1200	roughly a 2× number gap

(FEPA; Washington Mills, 2026; eQualle, 2026.)

The practical consequence is blunt: a "400-grit" FEPA disc and a "400-grit" CAMI disc leave different finishes. By the polishing range, a US/CAMI 600 is only about as fine as a FEPA P1200. Treating "600 grit" as one universal value across catalogues will mis-sequence a finishing job by several steps.

Why a grit number is a tolerance band, not a single size

There is a second, deeper reason cross-scale equivalence is only approximate: a grit is not one particle diameter at all. It is a size distribution with a defined median and an allowed spread, and each standard pins that distribution with its own tolerance band and tail limits (FEPA; Washington Mills, 2026).

• FEPA pins microgrits to the D50 (the median — 50% of grain finer, 50% coarser) with additional control points (informally the D3 oversize cap and D94 undersize limit) that cap the coarse and fine tails. The D3 oversize cap is the part that stops a single rogue coarse grain from leaving a deep scratch in a fine finish (FEPA F/P standards; Washington Mills, 2026).
• ANSI/CAMI specifies an average particle diameter for the distribution — a looser tolerance band than FEPA's, which is part of why two "120-grit" products from different makers are never identical, only similar.

This is also why reputable charts publish slightly different microns for the same number — expect ±10–15% chart-to-chart variation, widening at the fine end.

How each size class is actually measured

The measurement method changes at the macrogrit/microgrit boundary, which FEPA splits at roughly 53 µm (about P220/F220):

• Macrogrits (coarser than ~P220) are screen-graded — sized by sieving through a stack of test screens. The grit number maps to the midpoint sieve of the grading.
• Microgrits (finer than ~P240) are too small to sieve reliably and are graded instead by sedimentation (how fast the grain settles in a fluid), electrical-sensing-zone, or laser-diffraction methods (FEPA; UAMA Abrasives 101, 2026).

A grade measured by the wrong method for its size class — for example, a sieved "micron" number — is not verifiable against the standard. That distinction is the same evidence discipline that underpins how serious abrasive claims get backed; see how test data and ISO/IEC 17025 back abrasive claims.

The cross-standard reference table

Use this as a lookup, not a formula. These are nominal medians; expect variation that widens at the fine end.

FEPA-P	CAMI	JIS	~Micron (µm)
P120	120	120	~125
P180	180	180	~78
P220	220	220	~66
P320	240	320	~46
P400	320	360	~35
P600	400	500	~26
P800	400	600	~22
P1200	600	800	~15
P2500	1200	1500	~8

(FEPA; Washington Mills, 2026; eQualle, 2026. Japan's JIS R6001 scale sits between the two and is shown for completeness.)

Read the table the right way: FEPA-P and CAMI agree at P120/120, then split. By the time CAMI reads 400, the FEPA equivalent is already P600–P800. Note the divergence threshold is a band, not a hard line — treat ~P220 to P240 as the point where bare numbers stop being safe to compare, and always quote the micron equivalent through that band.

Why this matters on a real bench

The divergence is not academic. It is exactly the gap that "scale-switching" exploits. On commodity import abrasives, a bare printed number with no scale named is technically not a lie, but it is ambiguous — and the seller can quote whichever scale produces the highest, finest-looking number for the same physical grain.

The concrete trap: a "P400" sold as plain "400" is roughly 1.5× coarser than a real CAMI-400 finish, and a bare "600" can be about 1.7× coarser than a North-American buyer's mental model (eQualle, 2026; metallography.org, 2026). The buyer cannot measure micron size by eye, so the mislabel only shows up in use — as scratches deeper than the claimed grit should leave, or one sheet finishing finer than the next.

The same evidence-over-assertion principle runs through this category. Peer-reviewed work on wheel safety makes the point: Abrashkevych et al. (2022) found that the convenient even-stress-distribution assumption was in "complete discrepancy" with measured behaviour — a specification is only trustworthy when it is measured against a named standard, not assumed. An honest grit declaration does the same: it names the scale, conforms to a published tolerance band, and states the micron equivalent so the claim can be checked on sight.

For matching a named grit to the finish it should actually produce, our grit-to-surface-finish (Ra) chart maps grades to expected Ra.

How to label and buy without getting burned

1. Read the prefix. A "P" means FEPA. A bare number on a North-American listing usually means CAMI. No prefix at all is the ambiguous case — ask which scale.
2. Match the scale to the product family. Coated abrasives (sanding sheets, belts, discs, and the abrasive cloth on a flap disc) take the P scale. Bonded grinding and cut-off wheels take the F scale. An F-number printed on a flap disc's coated cloth is a category error that produces a wrong micron lookup even when the grading was clean.
3. Convert through a chart, never the raw number — especially above ~P220.
4. Prefer the micron equivalent when sequencing fine work. "P400 (FEPA), ~35 µm" pins the product to one place on the grit ladder and to a target finish without making the reader guess the standard.

The Whitby Abrasives recommendation

Whitby Abrasives sells into both the FEPA-P market (Canada and Europe) and the CAMI market (the US), so we treat the grading standard as a spec to publish, not a number to leave ambiguous. We specify the P scale for our coated lines — naming the grade and, where it helps, the micron median — so a buyer can catch a rival's CAMI-400-sold-as-bare-400 by eye. That is the spec-honesty wedge a value-tier supplier earns trust with: correct, named specs, not the lowest sticker price alone.

If you are buying coated abrasives where the finish has to be repeatable, two places to start:

• Shop sanding belts graded on a named P scale, so the next belt in the box behaves like the last one.
• Shop flap discs where the spec names the coated P-grit of the cloth — the dual-construction case where scale errors most often hide.

The obvious objection: isn't a value-tier price just code for an uncontrolled grit lot? It is the opposite. The uncontrolled lot is the one that prints a flattering bare number and lets oversized outliers average out on the label. A named, micron-stated grade is what makes a Consistent Cut and a Predictable Life possible at a working price.

Frequently asked questions

Is FEPA P400 the same as 400 grit sandpaper?

No. FEPA P400 has a median grain size of about 35 µm, while ANSI/CAMI 400 is finer, at roughly 14–23 µm. The two scales agree at coarse grits but diverge in the fine range, so the same printed number means a different grain on each scale.

What does the "P" in P400 mean?

The "P" prefix marks a FEPA-graded coated abrasive — the European and global standard for sanding sheets, belts, and discs. A number with no prefix on a North-American product is usually graded on the ANSI/CAMI scale instead.

At what grit do FEPA and CAMI stop matching?

They track closely down to about P220 / CAMI 220, then diverge progressively through the fine range. Treat roughly P220 to P240 as the band where bare numbers stop being safe to compare directly, and convert through a chart above it.

Why do different grit charts list different micron values?

Because a grit number is a distribution, not a single particle size. FEPA pins the median (D50) with tight tail caps, while CAMI specifies an average particle diameter with a looser band. That is why reputable charts vary by about ±10–15%, widening at the fine end.

Which scale should I use for flap discs?

The coated P-grit of the abrasive cloth. A flap disc is a coated abrasive on a bonded backing, so it is graded on the P scale (or its plain CAMI equivalent) — never an F-number, which belongs to bonded grinding and cut-off wheels.

How can I tell if a "grit" number is honest?

An honest grade names the scale (P or CAMI), cites and conforms to a standard, and ideally states the micron equivalent so you can verify it. A bare number with no scale, and a finish that does not match the claim in use, are the warning signs of an uncontrolled or scale-switched grade.

Sources

• FEPA — Standards (P/F grit definitions; P-prefix for coated abrasives; microgrit D50 with D3/D94 tail limits; macrogrit-by-sieving vs microgrit-by-sedimentation; ~53 µm macro/micro cutoff). https://fepa-abrasives.org/abrasives/standards/ (accessed 2026-06-26)
• Washington Mills (2026) — FEPA & ANSI Particle Size Conversion Charts (micron medians; FEPA P = D50, CAMI = average particle diameter; FEPA 42-1 / 43-1 / 43-2:2006). https://www.washingtonmills.com/resources/guides
• eQualle (2026) — Sandpaper Grit Conversion Chart: CAMI vs FEPA (P) vs Micron (fine-range divergence; US 600 ≈ FEPA P1200; FEPA-P runs higher than CAMI). https://equalle.com/blogs/woodworking/sandpaper-grit-conversion-chart-cami-vs-fepa-p-vs-micron-explained-60-3000-grit-guide
• metallography.org (2026) — Grit Size Conversion Chart (ANSI/CAMI ↔ FEPA-P ↔ micron cross-walk; CAMI 400 ≈ P800, CAMI 600 ≈ P1200, CAMI 1200 ≈ P2500). https://www.metallography.org/resources/grit-size-chart
• UAMA — Abrasives 101 (macrogrit screen-sizing vs microgrit sedimentation-sizing; ~60 µm cutoff). https://uama.org/abrasives-101/ (accessed 2026-06-26)
• Standards bodies referenced: FEPA 43-1:2006 / 43-2:2006 (coated P-scale); ANSI B74.18 (North American coated-grain grading).
• Abrashkevych, Y., Machyshyn, H., Marchenko, O., Balaka, M., & Zhukova, O. (2022). Mechanical strength increasing of abrasive reinforced wheel. Strength of Materials and Theory of Structures. DOI: https://doi.org/10.32347/2410-2547.2022.108.295-308 — evidence that abrasive specifications and safety margins must be measured against a named standard, not asserted.

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