A cooking show I was watching recently said for recipe substitution, 1/2 cup regular table salt equaled 1 cup kosher salt or vice-versa (I can't remember). Please explain.--Rose-Marie
Because kosher salt is made of larger grains which may also have air trapped inside, the total amount of salt per unit of measure is less. The common advice is to use twice as much kosher salt as called for in a recipe using table salt, or half as much table salt as is needed in a recipe using kosher salt.
Actually, it depends on what company manufactured the kosher salt. While table salt is fairly standard in its composition, kosher salt varies greatly in the way it is made. The following table shows the weight and sodium ranges for various types of salt each for a constant measure of one teaspoon. While some salts may also contain other chemicals, the amounts are too small to worry about here.
For some kosher salt, if you substitute two for one, you may end up with a product that is over-salted by quite a bit. In fact, for the more dense kosher salt, you would want to use only one quarter again as much as the amount of table salt called for in your recipe.
As you can see also, sea salt varies quite a bit. Depending on the source, you may want to use the same amount of sea salt as table salt, or up to about half as much again.
If at all possible, to avoid over-salting food, always use the lesser amount for your substitution and correct the seasoning later. For some applications such as brining meat, you need to get the salt concentration right and you can't tell until the cooking is done. In those cases, it is best to find a recipe that uses the type of salt you plan to use, or use the nutritional panel on the salt you have to calculate how much you need. Remember to be sure that the amounts being compared are the same, teaspoon to teaspoon for example, and then calculate the ratio based on sodium content. Note that this will not work for salt substitutes containing potassium or other ingredients, however.