P400 sandpaper
35 µm grain
P400 (FEPA) · about 320 grit (CAMI) · 0.035 mm average particle
What P400 is for
The clearest case of the mismatch. P400 is about CAMI 320, a full step coarser than the number suggests to an American reader, and this is the grit where people most often notice something is wrong.
The two scales
| FEPA (European) | P400 |
| CAMI (American) | about 320 |
| Average grain | 35 µm |
| Scales agree here? | No — P400 is about 25% coarser than a CAMI 400 |
A packet marked 400 in the United States is finer than one marked P400 in Europe. The P prefix is the tell, and it is easy to miss on a label — which is why a finishing schedule copied from an American source and followed with European paper comes out coarser than intended at every step.
Nearby grits
| FEPA | CAMI | Grain | Typically |
|---|---|---|---|
| P220 | 220 | 68 µm | The last grit most woodwork needs before paint or stain, and the point where the two scales still agree closely enough to substitute one for the other without noticing |
| P240 | 220 | 58.5 µm | The first grit of the finishing range rather than the preparation range, and the first where the two scales visibly part company: P240 falls between CAMI 220 and 240 and matches neither |
| P280 | 240 | 52.2 µm | Fine finishing on hardwood, and between coats of varnish |
| P320 | 280 | 46.2 µm | De-nibbing between coats |
| P400 | 320 | 35 µm | The clearest case of the mismatch |
| P500 | 360 | 30.2 µm | Fine finishing and light wet sanding |
| P600 | 400 | 25.8 µm | Wet sanding paint and polishing metal |
| P800 | 500 | 21.8 µm | Between coats on a high-gloss finish, and the start of the polishing range rather than the sanding one |
Frequently asked questions
Is P400 the same as 400 grit?
No. P400 is roughly CAMI 320 — the American 400 grit is finer than the European P400. The two scales agree up to about 180 and separate above it, so at this end a packet marked 400 and a packet marked P400 are genuinely different papers.
What grain size is P400?
An average grain of 35 µm — 0.035 mm. That figure is what the P number is defined by, which is why it is the reliable way to compare across scales.
What is P400 used for?
The clearest case of the mismatch. P400 is about CAMI 320, a full step coarser than the number suggests to an American reader, and this is the grit where people most often notice something is wrong.
What comes before and after P400?
Coming up from coarse, P320 (46.2 µm) and then this; the next step finer is P500 at 30.2 µm. Skipping more than one step leaves scratches the finer paper cannot remove — the usual cause of a surface that looks fine dry and terrible once finish goes on.