#1
I know D'Addario has a PDF that breaks a bunch of things down but I'm mostly looking to compare a few different gauges to different scale lengths. Is there some sort of calculator online that does the formula for you?

For example, .009 E string on a 27" scale length guitar compared to a .010 E string on a 25.5" scale length guitar.
#2
not that i know of but a difference in scale length is a couple of pounds at most

27" is baritone so if you were considering tuning to E standard on one then I'd get really light strings, .010's or less
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#3
Try this link:
http://www.mcdonaldstrings.com/stringxxiii.html

It will let you enter every parameter- it is just not that obvious.
The "top window" lets you select a couple of typical string set gauges, as well as scale length.
But below that you can enter each string guage individually, as well as what it is tuned to.
#5
Much appreciated.

To further the discussion, is there any reason NOT to try to get the string gauges to create roughly the same tension? From what I see there is a difference between wound and plain strings (would be great if someone could explain this).

I typically play on Dunlop .010's but the different gauges just don't feel right. My low E and G strings aren't tense enough and my high E is a bit too much. I'm hoping I can calculate what string gauges would give a similar "feel" as far as tension goes. I'm also looking at some slightly longer scale lengths (between 25.7" to 27").