Formula For Ampere & Size Of Cable When Gigging In A Small Club, How Powerful A Bass Amp Do You Need?

When gigging in a small club, how powerful a bass amp do you need? - formula for ampere & size of cable

For a band playing in a club of small and medium-sized rock, power amp, you need a guitarist to be heard? On the other hand, listen to an amplifier with much more powerful than the bass on the drums and guitar?

Not for my purposes (I) learn to play bass, it is a special formula for the power amplifier should be as low vis-à-vis a guitar amp?

Amplifiers that have been commonly used combos, but some were probably used amp with the front cabin.