I suggest you invent your own rule, because then you will have an understanding of that rule and it’ll be more relevant to you than another person’s invented value for such a strange concept. Also, unless you are in the soda business, what I expect you really want to know is how much sodium to consume per day, and therefore how much each food item contains, and not really whether each can of soda qualifies as “low sodium”. Any sodium will add to your daily total, which is what matters to the person. To that end, the US government recommended daily allowance for average folks seems to have dropped in 2004 from about 2400–2500 mg to 1500 mg . So, you can compare that to the sodium in all foods, including soda.