https://www.aafp.org/afp/2009/0715/p157.html
PLEASE DON'T EVER USE MAGNESIUM CITRATE - IS DESTROYS CERULOPLASMIN.
Calculate YOUR Elemental Magnesium baseline needs as 5mg/lb body weight.
Note that there are DIFFERENT formulations from manufacturers - so the elemental values in the chart should be considered estimates. Always read the labels on the products you are considering using.
An example of how to read a label:
Jigsaw Magnesium s/SRT (B-Free)
Dose: 4 tablets = 500mg Elemental Magnesium
Magnesium (as Dimagnesium Malate) 500mg
Malic Acid (as Dimagnesium Malate) 1436mg