today im picking up a new second hand sail, 6.8 north warp, I have a 30cm weed fin and another fin with suggested sail range on the side. is there a table you can copy laminate for your gear bag.

many factors to take into account
board width, volume, weight of sailor, etc

example: for my 8.x sails I use a 48 cm fin on my freeride and 56 cm on my JP SLW freeformula

here is a table from Select fins and there are others

ok seems to make sense all my fins are 30cm
don't quiet make sense of the graph, may be having a blond moment.

I have a 6.2, 6.5 and 5.4ish sails

Check out the riggeek website. They have formulas that take your weight into account.

According to Maui Fin Company, a lot with width of the board. According to them, we are choosing too small fins lately for our boards width. My friend chatted with them while they were testing fins for Naish boards. Funny however, when i try stock fins, I feel most of the time that I'm over finned!! ;-). They were saying, fins are now so well understood that it's will not spin-out. If you spine-out for no reason, you are under fin.

@ains :
based on your question ...

i made myself a chart of wind strength with sail size mapped against board with fin:
so, in 20 kph winds (~11 knots) i will use JP SLW92 with 10 m² sail and 66 cm Select slalom or 58 cm True Ames SB weed fin
and i put litres/width as a board indicator as well

you can also see that sails in 8.0-8.5 m² range can have fins from 30 cm to 58 depending on the board !!