baluns are transformers and the impedance ratio is related to the turns
ratio.

If you have a dipole antenna the centre feed point is about 75 ohms and if
you have 75 ohm coax the balun needs to be 1 : 1 .

If you have an end fed antenna the feed point can be anything from 600 -
1000 ohms so a 4:1 to 8:1 ratio matches the coax.

Bit of experimentation.

use the one that works best.

Feed point impedance depends on the frequency, so measurements, while
possible, tell you an exact answer to a question where close enough is an OK
answer.

Robert