This is Dr. Houser on magnesium:
"This is one which will depend upon the salt used. In other words – magnesium orotate has wonderful bioavailability but the orotic acid molecule is very large limiting the amount of elemental magnesium you get. If using something more common like magnesium oxide, you are talking about 2 oxygen molecules limiting the amount of elemental magensium to a much lighter degree. Magnesium oxide is our standardizing molecule where we would use about 400 mg per day to ensure adequate amounts, whereas magnesium orotate is about double this. Most other magnesium salts fall somewhere between the two.
Keep in mind this general rule of thumb when shopping for magnesium, the lower the amount of elemental magnesium, the higher the level of bioavailability (there are a few exceptions to this BUT that generally holds true)."
I personally take 400mg of magnesium glycinate. SNS MCC has 180mg of Magnesium?