Is there a way i can rougly estimate or some kinda formula that i can do a line conversion? What i mean is that if a reel says that if it can hold 240 yards on an 8lb test , if i put a 12lb test how much can it hold? I've tried to figure it out but, im just stumped.

it depends on the lines thickness.

If a spool can hold 60 yards of line that is .06" thick, then it can hold 30 yards of line that is .12" thick.

(atleast i think thats right)

You need to know the diameter, not the lb test of the lines. Divide the stated diameter by the new lines diameter. multiply this result by the stated yardage, and you get an answer in the ball park. Won't be exact, but close enough for government work.

Cheers,

GK