This year I'm thinking about switching to braid and FC leader for all my spinning rods.  I've been looking at sunline sx1 braid in 12 or 16#, but I can't find the diameter either of them are closest to in mono.  TW doesn't list it and neither did the sunline website.  Does anyone know?  I was thinking 16 on my 2500 and 12 on my 1000 size reels. 

You'll be fine with both. I don't know their diameters but they can't be too much more/less than say power pro. I run #20 on my 2500 and #10 on my 1000

It is a 4 strand PE.

Diameter in inches
10lb .0070
12lb .0075
16lb .0080
20lb .0100
30lb .0120
40lb .0130
50lb .0150

 

***NOT MY WORDS***

I use 15# on 2500 and 3000 Stradic FJs and 10# on Symetre FH 1000. Usually buy PowerPro or Spiderwire Stealth.

Braid is all I use for spinning reels and very rarely use a leader.

You should be able to find them on the website or at least on the image of the line. I know .27mm Sunline & P Line CXX comes to roughly .010. That's just shy of the 12lb mono that I use which is .013

10 lb. Sonic Braid on my spinning set up, no leader, if I do , I use TORAY super strong hard in 10#

Braid is more about line management than strength, braid breaks much higher than than what's on the label.  On small reels I'm using 10# braid, once I'm at a 4000 it's 15 or 20#.  As there is no stretch to braid and very little with a shock leader using your drag is important.  Too tight a drag with braid with a larger fish on will pop your knots.  I may add when having fish on too big to land or fear of exhausting the fish, a good procedure to break that fish off would be to grab the spool with your hand.

My Sunline Super FC Sniper box shows the diameter on the front of the box.

 

So look a the boxes on the web site to try to see the diameters.

This isn't the first time I tried this. The first time I used 10# Sufix and I kept breaking the leader off at the knot. I don't have any problems with the 20# and 6 or 8 # FC. I really just want something smaller for the 1000 size reel I've been using.