Braid, Backing, Capacity

How much braid do you want to end up with on a spool after the backing.
For instance I have a reel with a stated max capacity of 500 yards of 40 lb braid.
I put 30 lb braid on it. Target for me is to put about 300 yards on top of the mono backing.
The reel is for throwing plugs, metal and rubber (no bait), surf and bay side.

I put 150 on all my surf reels but my tuna reels they have 600 to 800 yards depending on the reel. cod reels have 300

Thanks for the info guys. I was using 100 because sometimes I get it in 100 yd packages. I see that is not enough if you account for abrasion and breakoffs.