Lately, I've seen sandpaper grits with a P in front of them. I used to just get, say, 400 grit. Now, there is P400. Are they the same? I looked it up and Wikipedia had some chart comparing grits with a "P" and ones without. It stated that one designation is US (without the "P") and the other is Euro/ISO (has a "P" in front).

It seems that all the sandpaper I've seen has a P in front of it. Did we switch over? Even stuff sold as "400 grit" says P400. They are not the same, according to the chart; P400 is closer to 320.

I'm wet-sanding my car and I'm using what I think is 800, but it has "P800" on the back. P800 is similar to 400.

Anybody got any insight?

Made in America paper is good. Made in China not so good. If you buy low cost paper from Amazon it is from China.

It is still ok just not the quality of USA stuff or German paper.

I am not certain the exact relationship, but the abbreviated story is that they are sort of similar. My impression with p320 (one I use a lot) being it is similar to 400 grit but a bit more aggressive. One thing I have found is that in many cases the sand paper wears out so quickly that walking from coarse to fine in succession is almost always worthwhile: the grit goes dull real fast.

Here's the chart:

Click to view attachment

At the higher numbers, the difference is pretty great.

The p denotes the euro standard for sandpaper. FEPA