i have a stradic 3000 wondering how much braided i need to fill it say with 20lb suffix braided

Err...I fill it to the top.
Remember if you've never used braid before, you have to put a few winds of mono on the spool first, then tie to the braid or it'll spin in the spool.

I use 2500's and a 150yd spool is more than enough with 30, but 20 will be a lot more on the spool...

do you have to put mono backing or can you just go strait braid or maybe just stick some duck tape to keep it from slipping when your trying to put new line?

are you saying I will need more line if i do 150yds of 20 lb braid?

The mono backing is also a cushion for the drag. Better reel life.

Your reel should have an indication of the number of yards of line it will hold. My Stradic 4000's have capacities in both line weight and line diameter. Check the diameter of the braid you are wanting to use and see how much of that diameter will fit on the reel by comparing it to the capacities listed on the reel. BTW the line diameter info is on the other side of the spool from the line weight capacities.

on shimanos site the braided and mono specs are different say 6lb mono has 280 yds or something like that and when using power pro at 20lbs test with 6lb diameter it says 140 yds. This is why Im confused

For the kind of fish you are targeting with a 3000 sized shimano, you won't ever need more than 150yds of 20lb braid. Just for reference, I was able to get 200yds of 30lb daiwa surf braid (same diameter as 20lb powerpro) on my 3000 stella fd. Just make sure you pack it down tight. If you're not sweating by the time you're done spooling up your reel, you didn't do it right.

You don't need a mono backing. Just learn to tie on correctly. Just choose a knot that gets tighter as you pull. An arbor knot is the basic for tying line to a spool. I just put some braid on one of my saltwater spools this morning. I would suggest mono backing for baitcasters though since they don't have the grooves to hang on to like spinners. Oh and about the quantity, read the reel. It tells you how much to use.

Use a mono backing!!!

I agree.

If you don't want to use a mono backing, don't put duck tape on your reel. It's a pain to get that sticky crud off your spool. Use teflon tape, it will come right off when you want it to. Personally, I think the mono backing works better.

One wrap of electrical tape.

One 150yd. spool of 30lb. braid.

Done deal.

Like stated above it all depends on the reel, I have a shimano saragosa 6000 with 300yards of 50lb power pro, with about 10yds of mono as a backing. Also like stated above wrap it tight.

I have a Penn, don't remember the model #, but it's one of the big salt water reels. I have about 100 yds of 65 lb power pro braid. I topped it off with 30 lb mono to the top. Maybe that's backwards, but it works for my purpose and where I fish. I have the power pro for strength, and for some distance if a really big fish runs. The 30 lb mono on top is not gonna break on a big fish, taking out line. But if there is a major snag, for whatever reason, I'd rather the 30 lb mono break, than losing the power pro.