You need to follow a recipe based on ratios. The web page I linked above suggests 5 parts mix to 2 parts calcium nitrate to one part epsom salt by weight.
That seems a bit off to me for our favorite cultivar, I'm running 2:2:1.
Dissolve the calcium nitrate in a different container than the rest, then mix once everything is in solution. I suggest making a stock solution of known strength with the mix.
If you keep the ratios correct, it doesn't matter exactly how much nutrient per gallon, you just dilute the mix to the desired EC. It's easier than it sounds.
For example, I ran my base mix stock solution at 200g/gallon. To get 100g, I just stirred it up and decanted a half gallon into a bucket. I added 50g of epsom salt, added a gallon or two of water, gave it a stir and let it sit to dissolve. In a separate bucket, I dissolved 100g of calcium nitrate with a gallon or two of water. Now I have my 2:2:1 ratio.
I'd start filling a 32 gallon trash can with water and dump the two buckets into it. My EC meter would start out reading high and would drop as I added more water. When I reached the nutrient strength I wanted, in my case around EC 2.3, I shut off the water and my nutrient solution was ready to use. It would end up being about 28 gallons. If I wanted a lower EC, that would of course mean more water. My pH always came out to 5.9-6.0 and thus didn't need adjusting. That's due to the ratio of ammonium to nitrate in the mix, something the manufacturer does for convenience.