Coarser salt doesn't yield automatic sodium savings.
It's conventional wisdom that big-grained salt contains about 25% less sodium by volume than table salt. The idea: Coarse crystals don't pack tightly and take up more space in a measuring spoon (with lots of air between them), meaning you consume less sodium. Labels on one brand show a 110mg difference between ¼ teaspoon of their table and kosher salts; that's a 19% savings if you use kosher. But our analysis of six salts showed less variation per ¼ teaspoon than you might think.
Bottom line: If you're watching sodium, you can't throw "gourmet" salts around with impunity.