sandpaper vs wetstone

[wisewood]

is there a difference between the classification of grit for sandpaper vs waterstones?

[cbwx34]

is there a difference between the classification of grit for sandpaper vs waterstones?

Yes.  Here's a brief definition of the different standards used...

FEPA (Fédération Européenne des Fabricants de Produits Abrasifs) Federation of European Producers of Abrasives. The FEPA distinquishes between grain for sanding paper (FEPA P) and grain for sharpening stones or wheels (FEPA F) The decisive factor for comparison is FEPA F. FEPA P is only used for sanding paper.
JIS (Japanese Industrial Standard) issued by the Japanese Standards Association.
ANSI American National Standards Institute.

... and a quick comparison chart can be found here...

http://www.washingtonmills.no/products/grit-sizes.html

... and a more extensive chart can be found here...

https://docs.google.com/spreadsheets/d/1VaTf3MXuwuvH-QLwOci4f9B9Zhkbuu1wjoSCZIUsR-o/edit#gid=0

If you really want to go down the rabbit hole, read this...

https://www.bladeforums.com/threads/the-grand-unified-grit-chart.856708/