I have a 706Z I never used and just decided to put some 20# fireline on it. I bought a 300 yard spool. Approz. how much mono. backing (say 10 #) can/should I put on it.

Thanks for the help!

just enough to cover the spool

I'd say about 30%-40% of the spool should be backing, depending on how full you like your spool.

I know the spool takes 300 yards of 20# mono which has a diameter of .018
If you divide the diameter of the Fireline by the diameter of the mono - then subtract that percentage from 1 that is the % of backing you need to fill the spool.
For example:
300yds X .018 = Full Spool
Say your braid has a diameter of .012 (hypothetically)
.012 /.018 = .66
1-.66=34% of spool backing needed
.34 X 300 = 102 yards of 20# mono backing needed

I'd say about 30%-40% of the spool should be backing, depending on how full you like your spool.

I know the spool takes 300 yards of 20# mono which has a diameter of .018
If you divide the diameter of the Fireline by the diameter of the mono - then subtract that percentage from 1 that is the % of backing you need to fill the spool.
For example:
300yds X .018 = Full Spool
Say your braid has a diameter of .012 (hypothetically)
.012 /.018 = .66
1-.66=34% of spool backing needed
.34 X 300 = 102 yards of 20# mono backing needed
Joe; That's some info you just gave us. Thanks. Jake.

300 yards of 20lb fireline will fill a 706 with just enough mono to fill a spool, trust me I've done it. Fireline is much thicker than most braids, also breaks substantially higher than its rated form, 30lb fireline has a diameter close to 20lb mono.

just enough to cover the spool

You'll come up short with 20. You can get 300 yards of 30# Fireline on a 706 spool with just enough mono to cover the arbor.

I also have a new Penn 706z so Mike are you suggesting that i get 30# Fireline and not 20#? Thanks

Agree with Mike P, 300 yds of 20# will not fill the spool if you just cover the arbor with mono. 30# will fill it completely and then some if you are unable to pack it really tight.

If you have more than one 706z, fill one with 20# fireline and then top it off with mono. Now transfer it to the other spool and it will be perfect.