No one can tell you how much you need.
It's individual. You'd need an in-person evaluation. You'd actually need a really scientific one. There are a couple of short cuts.
Do you sweat like a hog? I do.
When you sweat, does your sweat sting? Mine does. It's so bad that I have to wear a head band to keep the salty sweat out of my eyes.
When I'd train for long MMA workouts, I'd get exhausted towards the end. This wasn't due to lack of condition. It was hyponatremia. So I started adding salt to my workout shakes. Problem solved.
I need a lot of sodium:
I am at the far end of the spectrum; that is, I need a lot more sodium than most people. You may be at the tails or in the belly of the curve. Only you can figure that out.
So you sort of have to figure this out for yourself through diligent research, study, and self-observation.
If you know someone who really knows his shit, that would be helpful, too. This is rare.
It is amazing how LITTLE people know about electrolytes, even though obtaining the optimal balance for an individual is a major performance enhancer. How many people will even ask you, "Does your salt sting?" That is a basic question, yet you never hear "gurus" mention it. (Though some will now pretend as if the ALWAYS knew this stuff after reading one forum post.)
"Salt" me up, and my workouts will rock. Had I not added salts to my beverages and workout drink, I'd still be wondering why I "gassed" towards the end of my workouts.