CAMI, FEPA, and Micron: Build a Grit Conversion Sheet You Can Trust

A grit number is meaningful only with its grading system. CAMI numbers, FEPA P-grades, and micron values are related measurements, not three perfectly interchangeable labels. Use a conversion chart to choose a starting comparison, never as proof that two abrasives will leave identical scratches. Mineral shape, coating density, backing, wear, and test method still affect the result.

Keep the grading system attached to the number

Keep the prefix with the number. “P600” identifies a FEPA coated-abrasive grade, while an unprefixed 600 may refer to another system. A micron label describes a particle-size measure but still does not capture backing, mineral shape, coating density, wear, or the scratch produced in a particular process.

FEPA explains that coated abrasives use P-grades and that macrogrit size is specified as a distribution range rather than one exact particle diameter. Its standards overview also distinguishes coated-abrasive P grades from bonded-abrasive F grades. A chart that drops those prefixes discards essential information.

Use a conversion as a starting hypothesis

Record the exact label printed by the manufacturer, the standard named on the package or data sheet, the abrasive format, and the intended next step. Keep ranges when a source gives ranges instead of inventing one exact equivalent.

Do not turn a range into false precision. If one source shows an overlap, retain that overlap and its citation rather than publishing a single “exact equivalent.” When a package gives only an unprefixed number, consult the manufacturer instead of guessing the standard from the country of sale.

For a sheet-format option, 600-grit 10-sheet pack can be cut to a suitable hand block or detail support. The product link confirms the offered format and grade; it does not establish compatibility with an unknown coating, resin, stone, or finishing system.

A real product makes the record concrete: photograph its label and note whether the manufacturer prints a grading prefix. The linked sheet can be used in a suitable sanding test, but its nominal number does not certify equivalence to a micron film or to a product from another standard.

Validate the row on the work that matters

A shop log that writes only “600” cannot explain a finish change. “P600 film disc, dry, fresh” compared with “15-micron sheet, wet” preserves enough context to repeat the trial.

Prepare neighboring sample areas with the two candidate abrasives while holding support, pressure, passes, cleaning, and inspection constant. Compare the deepest scratches after the surface is clean and dry, then run the intended next step. The conversion is useful only if both samples reach that next step predictably.

A useful cheat sheet links every equivalence to its source and flags approximate rows clearly.

Date every chart and keep its sources. Product lines and labels can change, and a shop shorthand tends to outlive the evidence behind it. A modest chart with explicit uncertainty is safer and more repeatable than a large table of unsupported exact matches.