when going down in board size how mUch?

[1tuberider]

A starting point for low volume board would be to divide your weigh by 2 and add 10 to 20 for a reasonable
short board volume. I weigh close to 200 and my short board I ride is 120 ltr. I could go smaller but the dues
is higher and not worth it to me.

Your skill and balance may let you just divide by 2 but for me that would be pushing it. As far as working your way down
to that level, its not to overwhelming to start there. Just spend some time in flat water first and then challenge yourself. Maybe try to demo or borrow before you commit.

I do have a friend that could not do it even if the board volume were his weight. He has a balance problem and uses outriggers on his kayak.

[Twitchy]

I stepped down from a 9'2"x28" (120L) to a 8'3"x27 (90L) to a 7'4"x28" (85L).  I'm 72Kg.

Going from from the 9'2" to the 8'3" was tough for a handful of sessions.  Dropping to the 7'4" was only mildly challenging. 

I did demo the 7'4"x25.5" (78L) and it was tough.  Lumpy day and lots of falls.  On wave performance was very good though.