Diamond & CBN Grit Size Converter

Understanding Abrasive Grit Sizes

What is grinding wheel grit size?

Grit size describes the average particle dimension of abrasive grains used in grinding wheels, cutting tools, and lapping compounds. It determines surface finish quality, material removal rate, and heat generation. Coarse grits (large particles) remove material quickly but leave rough surfaces. Fine grits produce smooth finishes but cut slower. Grit designations vary by standard — FEPA (European), Mesh (US sieve), and micron-based systems each define particle size differently.

Diamond grit size explained

Industrial diamond abrasive grit sizes range from approximately 1 µm (microgrit for lapping) to over 2000 µm (coarse crushing grit). The FEPA D system designates diamond grit by the nominal average particle diameter in microns: D25 ≈ 25 µm, D64 ≈ 64 µm, D126 ≈ 126 µm. Diamond is the hardest known material, used for grinding cemented carbide, ceramic, glass, stone, and other hard-to-machine materials.

CBN grit size explained

Cubic Boron Nitride (CBN) is the second-highest-hardness abrasive after diamond. CBN grit sizes follow the FEPA F system for bonded abrasives: F36 through F1200. CBN excels at grinding hardened steels, cast iron, and superalloys where diamond would react chemically with ferrous materials. Common CBN grit sizes for precision grinding are F80 to F400, balancing removal rate with surface finish.

FEPA to Mesh Conversion — How the Systems Relate

FEPA (Federation of European Producers of Abrasives) defines grit by measured particle-size distribution using sieves and sedimentation. US Mesh is based on the number of openings per linear inch in a woven wire screen. A 60 Mesh screen has 60 openings per inch (~250 µm), while FEPA F60 also targets ~250 µm — but the measurement methods and tolerance bands differ. Cross-system comparisons should be treated as approximate.

Grit size vs surface finish

Finer grit produces smoother surface finishes. Typical relationships: coarse grits (F36–F60) yield Ra 1.6–6.3 µm; medium grits (F80–F220) yield Ra 0.4–1.6 µm; fine grits (F320–F1200) yield Ra 0.05–0.4 µm. Actual finish depends on workpiece material, wheel bonding, machine rigidity, coolant, and feed rate — grit size alone does not determine surface quality.

Grit size vs stock removal

Coarser grits remove more material per pass because larger grains create deeper scratches and higher cutting forces. F36–F60 grits are typical for rough grinding and stock removal rates above 10 mm³/mm·s. Medium grits (F80–F120) balance removal and finish. Fine grits (F220+) prioritize surface quality over removal rate. Selecting grit size is always a trade-off between productivity and surface integrity.

How to choose a grit size

Start with your primary requirement: fast stock removal → coarse grit; fine surface finish → fine grit; both → use a coarse grit for roughing and a fine grit for finishing. Consider workpiece material hardness (harder materials may need finer grits to avoid damage), required tolerances, thermal sensitivity, and economic factors. When in doubt, consult your abrasive supplier and start with a medium grit, then adjust based on results.