Scale length, if the tension would be the same?

[itu]

I have not started to calculate, in case someone has:

I prefer 40 - 100 sets for a 34" 4-stringer. How much longer should the scale be, if I used the same set for BEAD under similar tension?

[BigRedX]

To have the same tension with the same gauge strings you would need to add another 5 frets worth of neck. That would put the octave at B on what was the E string. The distance from the 7th fret to the bridge on a 34" scale bass is 22.5". 

Therefore your B-D bass with the same gauge string at the same tension would need a scale length of 45"

[itu]

Thank you, Sir, very good, this sounds very reasonable. I was on the right track.