Sandpaper Grit Chart (FEPA P grit → particle size)

Understanding the sandpaper grit chart — concept and principle

This chart turns a European FEPA "P" grit number, the one printed on the back of most sandpaper sold in Korea and Europe, into the average abrasive particle size in micrometres (µm) and a typical job for that grit. Use it to plan a sanding sequence for wood, paint, metal or car bodywork and to compare papers from different makers.

How it is calculated

There is no formula to type in: the grade is looked up in the FEPA table. Each P number corresponds to a defined particle size distribution, and the chart shows its average (median) diameter. The table runs from P40 (about 425 µm, heavy stock removal) to P2500 (about 8.4 µm, final polishing). As a rough rule, the particle size halves when the grit number roughly doubles in the fine range, for example P400 at 35.0 µm and P800 at 21.8 µm.

The principle

Grit numbers began as sieve counts: coarse grains are those that pass through a screen with that many openings per inch, so a higher number means a finer mesh and smaller grains. For coarse grades (P12 to P220, ISO 6344-2) the size is still checked by sieving; for fine grades (P240 to P2500, ISO 6344-3) the grains are too small for sieves and are graded by sedimentation, measuring how fast they settle. Smaller grains cut shallower scratches, which is why you work from coarse to fine: each grit removes the scratches of the one before it.

Worked example

Default input: P180.

1. Find P180 in the FEPA table.
2. Read the average particle size: 82 µm (0.082 mm).
3. Read the typical use: light sanding between coats.
4. Result: P180 → 82 µm, used between coats.

How to read the result

• Above about 200 µm (P40–P80): fast removal of material or old finish, leaves deep scratches.
• About 100–160 µm (P100–P150): smoothing and preparing bare wood.
• About 35–82 µm (P180–P400): between coats and before finishing.
• Below about 26 µm (P600 and finer): wet sanding of paint, polishing preparation and final polish.

A normal sequence skips no more than about one or two steps (for example P80 → P120 → P180) so that each grit can fully erase the previous scratches.

Common mistakes

• Treating US CAMI numbers and FEPA P numbers as identical. They are close up to about 220 but differ for finer grits, where a CAMI number is generally finer than the same P number.
• Jumping straight from very coarse to very fine paper; the deep scratches remain.
• Continuing with clogged paper, which burnishes instead of cutting.

FAQ

Frequently asked questions

What particle size is P400?

About 35.0 µm on the FEPA P scale.

Which grit should I use between coats of paint or varnish?

P180 to P320 is a common range for de-nibbing between coats; use lighter pressure on thin finishes.

Why does finer paper have a bigger number?

The number came from sieve openings per inch; more openings means smaller holes and smaller grains.

Sources: ISO 6344-2, Coated abrasives — Grain size analysis — Part 2: Macrogrits P12 to P220 · ISO 6344-3, Coated abrasives — Grain size analysis — Part 3: Microgrits P240 to P2500 · FEPA Standard 43-1, Grains for coated abrasives