Total Body Water and Fluid Compartments by Age and Sex

Total Body Water (TBW)

The total amount of water in the body expressed as a percentage of body weight.

Intracellular fluid (ICF)

The fluid contained within cells, constituting 63% of total body water.

Extracellular fluid (ECF)

The fluid outside of cells, constituting 37% of total body water.

Plasma volume

The volume of fluid in the circulatory system, calculated as one-third of the extracellular fluid.

Normal Sodium (Na+) values

135 - 145 meq/L

Normal Potassium (K+) values

3.5 - 5.0 meq/L

Normal Chloride (Cl-) values

98 - 107 meq/L

Normal Bicarbonate (HCO3-) values

22 - 26 meq/L

Normal Calcium (Ca2+) values

8.5 - 10.5 mg/dL

Normal Phosphorus values

2.5 - 4.5 mg/dL

Normal Magnesium (Mg2+) values

1.8 - 3.0 mg/dL

Normal Osmolality values

285 - 295 mosm/kg

Mass conversion for Sodium (Na+)

23 mg = 1 meq

Mass conversion for Potassium (K+)

39 mg = 1 meq

Mass conversion for Chloride (Cl-)

35 mg = 1 meq

Mass conversion for Bicarbonate (HCO3-)

61 mg = 1 meq

Mass conversion for Calcium (Ca2+)

40 mg = 1 mmol

Mass conversion for Phosphorus

31 mg = 1 mmol

Mass conversion for Magnesium (Mg2+)

24 mg = 1 mmol