For my single package hive this year I mix two cups of water and two cups of sugar in a quart pyrex measuring cup, stir until dissolved, then pour into the hivetop feeder. They usually clean it up in a day, two if it's cold, and that way I don't have to worry about how long it lasts. I may make a larger amount later on when there are more bees in the hive, but it's still the same principle.
Equal weight, and since sugar is close to the weight of water per unit volume, equal volumes work fine. The exact ratio isn't critical in any way, and the bees don't care. A little apple cider vinegar helps preserve it and makes it more attractive to the bees, but I don't like to put on more than they will use in a few days since I have only one hive to feed.
If I had dozens, I'd use HBH or vinegar all the time and feed four gallons per hive every time just to keep the work down.
Peter