Abrasive Grit Chart for Metalworkers: Which Grit for Grinding, Blending & Finishing

Quick Answer

For metalwork, grind and knock down welds at P40–P60, blend and shape at P80–P120, pre-finish at P150–P240, and finish or polish-prep at P320 and up. These are FEPA-P (coated) grits. Above roughly P220 the FEPA-P and ANSI/CAMI scales diverge, so always confirm which scale a grit number is on before comparing.

How to read an abrasive grit chart

Grit is the size designation of the abrasive grain bonded to a disc, belt or sheet. Lower numbers are larger grains that cut fast and leave deeper scratches; higher numbers are smaller grains that leave a smoother surface. A typical metalworking job steps down through several grits — coarse for stock removal, then progressively finer to refine the surface.

The number is rooted in sieve-mesh classification: historically it came from the number of openings per linear inch in the sieve the grain just passes through, so a finer mesh (more openings) yields a higher grit number and a smaller grain. Once grains get too small to sieve reliably — the microgrit range — grading switches to sedimentation or electro-resistance methods that measure the grain directly in microns (Washington Mills, 2026).

Two practical rules matter before you read any chart. First, the grit number names a size distribution, not one particle diameter — a median (d50) plus an allowed spread and tail limits — so two "120-grit" products from different makers are never identical, only similar (FEPA). Second, the standard the grit was graded against changes what the number means, and that is where most cross-border confusion starts.

Which grit for grinding, blending and finishing (metalwork)

The table below is the working chart for metal. Grit numbers are on the FEPA-P scale; the indicative Ra (arithmetic surface roughness) is a starting point, not a guarantee — actual finish depends on material, pressure, lubrication, machine and how worn the abrasive is, and a critical finish is confirmed with a profilometer (Alves, 2015).

(Ra bands from the WA grit-to-finish crosswalk, FEPA-P; µin ≈ µm × 39.4.) The bands overlap at the edges on purpose — belt speed, pressure and grit size each shift measured roughness independently, and in one controlled sanding study grit size was the only factor that significantly affected both surface roughness and workpiece temperature (Alves, 2015). Treat the chart as a selection guide, then verify the result against the drawing callout.

Don't skip more than one grit step

The governing rule for a clean finish is to never skip more than one grit step — 80 to 120 is fine, 80 to 220 is not. A finer abrasive physically cannot reach the bottom of a coarser grit's scratch valleys, so skipping leaves buried "ghost" scratches that telegraph through stain, plating or clearcoat. Choose the band that brackets your target finish, then reach it through a disciplined ladder.

Match the grit to the grain and the metal

Grit answers "how coarse," but the grain mineral answers "how hard and how long it lasts" — and the two decisions interact with the metal you are cutting. A coarse grit on the wrong grain still glazes or burns on stainless. See our companion guide to choosing the abrasive grain by material before you lock the grit ladder for a job.

The "400 grit isn't always 400" problem: FEPA-P vs CAMI vs JIS

This is the single biggest pitfall in any grit size chart. FEPA-P (Europe and most of the world, coated abrasives), ANSI/CAMI (North America, governed by ANSI B74.18), and JIS (Japan) are independent grading systems that were never designed to share one number line. They agree closely at coarse grits — at roughly P220 / CAMI 220 / JIS 220 and below the three are near-interchangeable — then diverge progressively through the fine range, with FEPA-P numbers running higher than CAMI for the same particle size (eQualle; Washington Mills, 2026).

Cross-standard grit equivalence: the scales track closely at coarse grits, then fan out in the fine range — so a bare grit number is ambiguous above ~220.

(FEPA; Washington Mills; eQualle, 2026 — nominal medians; expect ±10–15% chart-to-chart variation, widening at the fine end.)

The takeaway: a "400-grit" FEPA disc and a "400-grit" CAMI disc leave different finishes, and by the polishing range a US/CAMI 600 is only about as fine as FEPA P1200. Treating "600 grit" as one universal value across catalogues will mis-sequence a finishing job by several steps. We unpack this fully in why "400 grit" isn't always 400 grit.

Coated "P" grit vs bonded "F" grit

One more distinction that catches buyers out: FEPA uses P-grit for coated abrasives (sandpaper, flap discs, fibre discs, belts) and F-grit for bonded abrasives (grinding wheels, cut-off wheels). A P-grit and the same-number F-grit are not the same particle size (Washington Mills, 2026). Flap discs and sanding belts are graded on the P-scale; grinding and cut-off wheels on the F-scale. Keep the prefix correct when you cross-shop.

Why a grit chart only holds if the grit is graded honestly

Every band in the chart above assumes the grit is truly graded to standard. The reason FEPA-P fine grades hold a tighter, statistically defined tolerance than CAMI is the cap on coarse outliers — FEPA pins microgrits to the d50 median with d3/d94 tail limits, exactly the control that stops a single rogue coarse grain from leaving a deep scratch in a fine finish (FEPA). A value-tier abuse is the silent number-swap: selling a coarser or scale-switched grain under a finer number to look more aggressive on paper. That breaks the grit-to-finish mapping and produces "scratchier than described" complaints.

Research backs the principle that the grit's own characteristics — not just the workpiece — set which wear mechanism dominates, so consistent grit grading is what makes performance predictable rather than a roll of the dice (Rajendhran, 2023). For a target-finish view of the same data, see our grit-to-surface-finish (Ra) chart.

The Whitby Abrasives recommendation

Whitby Abrasives is a value-tier, Canadian-stocked distributor whose wedge is correct specs and test data, not the lowest sticker price alone. We grade to standard and state the scale, so the grit number on the box matches the finish on the metal — the difference between an honest chart and a bare number printed by a cheap import. Pair this chart with the right product format: reach for flap discs for the P40–P120 grind-and-blend bands, sanding belts for controlled progression on flat and contoured work, and resin fibre discs for aggressive coarse-grit stock removal. The common objection — that value-tier means low quality — is exactly what spec-honest grading and a stated grading standard answer: industrial-grade consistency without paying premium-brand markup, and no premium grain wasted where a correctly specified one does the job.

Frequently asked questions

What grit should I use for grinding metal?

For grinding and heavy stock removal on metal — knocking down welds, stripping rust or paint — use a coarse grit in the P40–P60 range (FEPA-P). This removes material fast and leaves a deep scratch pattern around Ra 3–5 µm, which you then refine with progressively finer grits.

What grit do I use to blend a weld?

Blend welds at P80–P120 (FEPA-P). That range removes the coarse grinding scratches and feathers the weld into the surrounding metal at roughly Ra 1.5–3 µm, ready for a pre-finish step before any coating or plating.

Is a 120-grit FEPA disc the same as a 120-grit CAMI disc?

At 120 grit, yes — FEPA-P, CAMI and JIS agree closely at coarse grits down to about 220. They diverge in the fine range: by the polishing end a US/CAMI 600 is only about as fine as FEPA P1200, so above ~220 you must convert rather than match the bare number.

Why does my finish still show scratches after going to a fine grit?

Most likely you skipped more than one grit step. A finer abrasive cannot reach the bottom of a coarser grit's scratch valleys, so the earlier scratches stay buried and telegraph through. Never skip more than one step — for example, 80 to 120 is fine, 80 to 220 is not.

Does grit number alone determine the surface finish?

No. The grit sets the band, but measured roughness also depends on material, pressure, belt or wheel speed, lubrication and abrasive wear. In a controlled sanding study, grit size was the dominant factor on both roughness and temperature (Alves, 2015), but a critical finish should still be verified with a profilometer, not assumed from the number.

What is the difference between P-grit and F-grit?

FEPA uses P-grit for coated abrasives — sandpaper, flap discs, fibre discs and belts — and F-grit for bonded abrasives like grinding and cut-off wheels. A P-grit and the same-number F-grit are not the same particle size, so keep the prefix correct when comparing a disc to a wheel.

Sources

• Washington Mills — FEPA & ANSI Particle Size Conversion Charts (FEPA-P and CAMI micron medians; macrogrit/microgrit cutoff; P vs F grit; P400 ~35 µm vs CAMI 400 ~23 µm), 2026 — https://www.washingtonmills.com/resources/guides
• FEPA (Federation of European Producers of Abrasives) — Standards: P-grit (coated) and F-grit (bonded) definitions; microgrit d50 with d3/d94 tail limits — https://fepa-abrasives.org/abrasives/standards/
• eQualle — Sandpaper Grit Conversion Chart: CAMI vs FEPA (P) vs Micron (fine-range divergence; US/CAMI 600 ≈ FEPA P1200), 2026 — https://equalle.com/blogs/woodworking/sandpaper-grit-conversion-chart-cami-vs-fepa-p-vs-micron-explained-60-3000-grit-guide
• UAMA — Abrasives 101 (macrogrit screen-sizing vs microgrit sedimentation-sizing; ~60 µm cutoff) — https://uama.org/abrasives-101/
• ISO 6344-2:2021 and ISO 6344-3:2021 — Coated abrasives, grain size (macrogrit P12–P220; microgrit P240–P5000) — https://www.iso.org/standard/78220.html
• ANSI B74.18 — North American coated-abrasive grain grading (CAMI scale)
• Alves, M.C.S. et al. (2015). Effects of belt speed, pressure and grit size on the sanding of Pinus elliottii wood. CERNE. DOI: 10.1590/01047760201521011216 — https://doi.org/10.1590/01047760201521011216
• Rajendhran, N. et al. (2023). Influence of grit particles characteristics on the abrasive wear micro-mechanisms of NbC-Ni and WC-Co hard materials. International Journal of Refractory Metals and Hard Materials. DOI: 10.1016/j.ijrmhm.2023.106422 — https://doi.org/10.1016/j.ijrmhm.2023.106422