Always measure by weight. Whether you're baking or brining meat or fish weights rule.
Brine recipes which call for a specific volume of salt, such as 1 cup of kosher salt in half a gallon of water, are less accurate and predictable than brine recipes which call for a specific weight of salt, because different kinds and brands of salt have different densities. If you check the volume-to-weight conversion tables for salt in various books and internet sites, you get a pretty wide range of weights for a cup of regular table salt. 10 oz./cup is about in the middle of the range of weights for table salt. Warren Anderson's book "Mastering the Craft of Making Sausage" lists weights of 22 grams/tbsp (i.e. 12.4 oz./cup) for regular salt and 12 grams/tbsp (i.e. 6.8 oz/cup) for kosher salt. amazingribs.com contains the following conversion table for different kinds of salt:
1 tsp Morton's tables salt equals:
1.5 tsp Morton's kosher salt
1.8 tsp Diamond Crystal brand kosher salt
1.8 tsp Morton's pickling salt
3 to 4 or more tsp sea salt
Unfortunately, many brine recipes specify a volume measurement rather than a weight for salt. In order to convert the volume measurement to a weight, you need to figure out what kind of salt the recipe specifies, and then choose an appropriate conversion factor.
I avoid this problem by standardizing the salt concentration (i.e. the water and salt components of the recipe) at 60 degrees Salometer. This allows me to ignore the salt volume measurement specified in the recipe and calculate the weight of salt required using a brine table.