Though my first post on this thread was, as is my usual habit, a smartass one (hey, those of us without knowledge turn to jesting...but, I digress...), I put new vacuum tubing in my whole car during the restoration - but I bought the stuff a little at a time as I got to whatever needed it, and didn't pay attention to the total footage I put in. I bought a color-coded set of the A/C-Heater stuff inside for the factory A/C only because it came with the schematic *hanging head* and had the installation instructions there so I didn't have to try and figure out how to connect everything (all my internal vacuum lines for the a/c and heater were missing when I started on my basketcase-turned-kick-ass-cat.
Sooooo...though I am still of absolutely no help to you, I have to agree with those that have posted and recommended guesstimating and/or just buying a spool (since it seems to need replacement at regular intervals *grrrrr*).
Ain't there ANYONE making good rubber that lasts these days (I mean BESIDES Trojan)