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Calculator: Fractional excretion of magnesium (conventional units)*

Calculator: Fractional excretion of magnesium (conventional units)*

Urine Mg  
Plasma Mg  
Urine Cr  
Plasma Cr  

Important: Inputs must be complete to perform calculation.

Decimal precision  


  • The fractional excretion of magnesium (FEMg) can be calculated by entering the values from simultaneously obtained urine and blood samples.
  • Please refer to UpToDate topic review of hypomagnesemia for a discussion of the interpretation of the fractional excretion of magnesium.
  • Cr: creatinine.
  • In this calculator, mcg is the abbreviation for micrograms.
  • * This calculator uses conventional units (also known as US units and gravimetric units) as the default for inputs. Do not use this calculator if you are using SI units (Système international d'unités); please refer instead to the SI units version of this calculator.

Equations used
FEMg = 100 * (Urine_Mg * Plasma_Cr) / (0.7 * Plasma_Mg * Urine_Cr)


Only digits 0 to 9 and a single decimal point (".") are acceptable as numeric inputs. Attempted input of other characters into a numeric field may lead to an incorrect result.

Information on this page may not appear correctly if printed.

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All information contained in and produced by the EBMcalc system is provided for educational purposes only. This information should not be used for the diagnosis or treatment of any health problem or disease. THIS INFORMATION IS NOT INTENDED TO REPLACE CLINICAL JUDGMENT OR GUIDE INDIVIDUAL PATIENT CARE IN ANY MANNER. Click here for full notice and disclaimer.

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