Here's my quick and dirty "no measure" method:

I use 2-qt rectangular GladWare or ZipLock re-usable/disposable containers. Pour in 1/2 cup non-iodized salt. I got the huge bag at Costco for $3.00) and keep a 1/2 cup scooper in there. Fill half way with COLD water. Make 3 quick passes of Mrs Stewart's bluing across the container with a good stream. Stir. Add semi-frozen herring (thaw just enough to separate them without losing scales) and fill with enough herring till the lid just fits. For the blue label baits I prefer, that means 12-16 baits, depending on the actual size of the herring. Remove lid, fill to the very top with more COLD water, and replace lid so there is no air gap. Turn container 3 or 4 times to stir. That's it!

I brine baits the night before and set all of my containers in a cold ice chest in the boat, ready to roll in the am. Baits are nice and firm when I am ready to fish. I open only one container at a time so the rest stay good and cold. I budget about 10 baits per person on board. That usually leaves a few spares for pesky sharks or clumsy feet and still allow you to fish about an hour per bait, although they are generally tough enough to get 2 or more hours per bait.

If it looks like we could be running low as the day wears on, I stretch the supply by "re-charging" baits with an injection of sardine or herring oil. I steer clear of "funky" scents. BTW how did garlic ever become so damn popular?

I once fished 3 days side by side with a buddy who used my brine, except unbeknownst to me, he laced his entire supply of herring with GARLIC! I scored double digits each day, and their boat could hardly buy a bite a day. At the end of their trip, he offered me a large container of his "leftover" brined bait. When I opened it up, it smelled like a Korean restaurant! No wonder they didn't catch any fish! I threw it all out when he was gone.