Magnesium Comparison Calculator

This calculator shows why the milligrams on a magnesium label are not the milligrams you get. Tablet Size is the total weight of the magnesium compound; the engine first multiplies it by the form's elemental fraction — oxide is 60 percent magnesium by weight, citrate 16, glycinate 14, taurate 9, and threonate just 8 — to get Elemental Mg. It then multiplies again by an absorption rate to get Effective Dose, and here the ranking inverts: oxide absorbs at only about 4 percent, while citrate absorbs at 28, glycinate at 23, and threonate and taurate at 18. The practical consequence the numbers expose is striking — a 400 mg oxide tablet yields 240 mg elemental but only about 10 mg effective, slightly less than the 18 mg a same-size citrate tablet delivers from a quarter of the elemental content.

Because both conversion factors are properties of the form, the Magnesium Form dropdown drives everything qualitative: it alone sets Absorption Rate and the Best For code, and at any one tablet size it can swing Effective Dose several-fold — swapping forms at a fixed 400 mg tablet moves the result nearly threefold. But across its own full 50-1000 mg range, Tablet Size is actually the bigger lever on Elemental Mg and Effective Dose: sweeping it end to end moves Elemental Mg by up to 570 mg (at oxide's 60 percent fraction) and Effective Dose by up to 43 mg (at citrate's 28 percent absorption), both larger than Magnesium Form's own biggest swing (520 mg and 31 mg respectively, each measured at the 1000 mg tablet size). Tablet Size scales Elemental Mg and Effective Dose linearly within whichever form you picked. Not modeled: dose-splitting, food effects, or individual gut variation.