The National Dairy Council (NDC) says that “generally, salted butter contains 1.6–1.7 percent” salt. But it’s up to each company to determine how much it wants to use in its product.

We surveyed the sodium content per tablespoon in a few brands, and the amount varies (note that salt itself has a sodium content of only around 40 percent by weight):

• Kerry Gold: 50 milligrams
• Land O’Lakes: 95 milligrams
• Challenge: 90 milligrams
• Safeway O Organics: 90 milligrams
• Straus: 45 milligrams
• Horizon: 115 milligrams
• Lucerne: 90 milligrams

If sodium in your diet is a concern, buy unsalted butter. If it’s not, then the choice is mostly a matter of taste. Most recipes call for unsalted (or sweet) butter. Also, the shelf life differs between salted and unsalted butter, says the NDC, because the salt acts as a preservative. The NDC says that salted butter can be stored for up to two months in the refrigerator and six to nine months in the freezer, whereas unsalted butter should only be refrigerated for up to two weeks and frozen for up to five months.