Why isnt my salt about 39% Sodium?
Minerals, naturally found in salt whether it's mined or evaporated; and believe it or not, water. Infosa In the US, the FDA requires that salt must not contain more than 2.5% minerals other than NaCl and still call itself salt. That 2.5% does not include water. HowStuffWorks Your numbers for sodium content seem a bit low, but not extremely so, especially for a very unrefined, wet salt. The more refined the salt, the less trace minerals it will contain.

Outside the US, it's possible that your salt also contains added iodine, fluoride, folic acid and/or anti-caking agents, but in the US those would be listed among the ingredients, and would be included in that 2.5%. Only iodine and anti-caking agents are common in the US.

Plus, nutritional information labels have legal margins of error. If and when they can, they'll be slick. Lower sodium looks good on a nutritional label.