Comparing Abrasive Systems

It is all very well to say that sandpaper is 100, 200, 600 grit etc, but what does it actually mean? When you talk about waterstones being 1000, 2000, 6000 etc, is that the same as 1000, 2000, 6000 sandpaper?

Unfortunately no! The way that I prefer to ensure I’m comparing apples with apples is to look at the size of the abrasive material itself. This at least should be a uniform way of comparing different abrasives. In other words, I may start sharpening on a diamond stone, transfer to sandpaper, and finish on waterstone. Ok, I may not jump around like this, but there is no reason why you can’t, once you understand the micron size of the abrasive.

I’ve listed here the 2 main sandpaper designations, and the actual micron size of the particles. This will then allow other mediums to be compared.

	ISO/FEPA Grit designation	CAMI Grit designation	Average particle diameter (µm)
MACROGRITS
Extra Coarse (Very fast removal of material)	P12		1815
	P16		1324
	P20		1000
	P24		764
		24	708
	P30		642
		30	632
		36	530
	P36		538
Coarse (Rapid removal of material)	P40	40	425
		50	348
	P50		336
Medium (sanding bare wood in preparation for finishing)		60	265
	P60		269
	P80		201
		80	190
Fine (sanding bare wood in preparation for finishing)	P100		162
		100	140
	P120		125
		120	115
Very Fine (final sanding of bare wood)	P150		100
		150	92
	P180	180	82
	P220	220	68
MICROGRITS
Very Fine (sanding finishes between coats)	P240		58.5
		240	53.0
	P280		52.2
	P320		46.2
	P360		40.5
Extra fine		320	36.0
	P400		35.0
	P500		30.2
		360	28.0
	P600		25.8
Super fine (final sanding of finishes)		400	23.0
	P800		21.8
		500	20.0
	P1000		18.3
		600	16.0
	P1200		15.3
Ultra fine (final sanding of finishes)	P1500	800	12.6
	P2000	1000	10.3
	P2500		8.4

Waterstones micron sizes are:

1000 : 14
2000 : 7.5
4000 : 3
6000 : 2
8000 : 1.2

So from this we can see that a 1000 waterstone is actually comparable to between a 1200 and 1500 grit sandpaper. And that my 6000 grit waterstones are VERY smooth!