Salt is a mineral composite of sodium and chloride. According to a report from the Massachusetts Department of Health and Human Services, the only difference in different types of salt is the size of the grain and how they are processed. Sea salt comes from the evaporation of seawater and contains trace minerals based on the original water source. Kosher salt is a product that has only sodium plus chloride. Kosher salt tends to have a larger crystal composition than sea salt. Nutritionally, both salts are the same. The larger size of kosher salts means you must convert the measurement to fit a recipe that calls for sea salt or the end product will taste wrong.
Read the kosher salt package to determine a proper conversion for the product. In many cases, the amount of kosher salt will exceed the necessary sea salt slightly. For example, the website for Morton Salt supplies a conversion table that suggests you use 1 1/4 teaspoon of kosher salt for every 1 teaspoon of sea salt.
Pour out the required amount of salt based on the recipe. For instance, if the recipe asks for 1/2 cup course sea salt, pour 1/2 cup kosher salt instead.
Add the additional salt needed to complete the conversion based on the table provided with the kosher salt. In the 1/2-cup example, you would add an additional 2 tablespoons of kosher salt, according to the Morton conversion formula. For 2 cups, you would include an additional 1/2 cup of kosher salt with the recipe.