Coated Abrasive Grit Chart

What it is

Coated abrasives (sandpaper, belts, discs) are graded by grit size. Two scales are common:

• P-grade (FEPA), set by ISO 6344. Marked with a P before the number, such as P120. Used worldwide.
• CAMI, set by ANSI B74.18. Marked with the number alone, such as 120. Used mainly in the US.

A higher number means a finer grit on both scales. In coarse and medium grits the two scales are close. In fine grits a P number is higher than the CAMI number for the same particle size.

How to read it

• Check the back of the product for a P prefix. If there is none, it is likely CAMI.
• Work through the grits in steps. Skipping too many steps leaves deep scratches the finer grit cannot remove.
• Use the chart to match a CAMI process to P-grade products, or the reverse.

Grit comparison chart

Above about 220 the match is approximate. Check the maker's chart or the average particle size if the finish is critical.

Key points

• Grit is only one factor. Mineral type (aluminum oxide, zirconia, ceramic, silicon carbide), backing and coating density also affect cut and finish.
• Microfinishing films and some fine products use micron grades instead of grit numbers.
• Grinding wheels use a separate grit system marked in the wheel specification.

Common mistakes

• Treating P400 and CAMI 400 as the same grit.
• Jumping from 80 straight to 220 and leaving deep scratches.
• Using a worn abrasive, which burnishes instead of cutting.

Governing standards: ISO 6344 (FEPA P-grade grit sizes); ANSI B74.18 (CAMI grading of coated abrasives); abrasive maker data.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.