Sodium Unit Converter
Sodium Unit Converter
Convert sodium between mmol/L, mEq/L and mg/dL. Sodium is monovalent, so mmol/L and mEq/L are the same number — and the mg/dL column is the one that needs care.
Sodium converter
Monovalent — mmol/L = mEq/LSodium 140 mmol/L
Formula and conversion factors
mg/dL = mmol/L × 2.299
mEq/L = mmol/L (sodium is monovalent)
- 0.434976
- 10 ÷ 22.99, the atomic mass of sodium — a decilitre is a tenth of a litre, so mg/dL × 10 ÷ MW gives mmol/L
- mEq/L
- milliequivalents count charge, millimoles count particles. Sodium carries one charge, so the two figures are identical
- why mg/dL is offered
- no clinical laboratory reports serum sodium in mg/dL; the unit is here for dietary, food-label and older literature values
- salt is not sodium
- 1 g of sodium chloride contains 393 mg of sodium — a factor of 2.54, and the commonest slip in dietary sodium arithmetic
Worked example
Sodium 140 mmol/L
140.0 mmol/L — the unit almost every laboratory reports
140.0 mmol/L = 140.0 mEq/L — sodium is monovalent, so the two are the same number
140.0 ÷ 0.434976 = 321.9 mg/dL, the mass unit used on food labels and in dietary work but never on a serum report
Within the adult reference interval of 135–145 mmol/L
The same sodium in three units
| mmol/L | mEq/L | mg/dL | |
|---|---|---|---|
| Adult reference interval | 135 – 145 | 135 – 145 | 310 – 333 |
| Hyponatraemia | < 135 | < 135 | < 310 |
| Severe hyponatraemia | < 125 | < 125 | < 287 |
| Hypernatraemia | > 145 | > 145 | > 333 |
Where milligrams of sodium actually appear
| Quantity | Sodium | In millimoles |
|---|---|---|
| 1 g of salt (sodium chloride) | 393 mg | 17.1 mmol |
| 1 g of sodium | 1,000 mg | 43.5 mmol |
| UK adult daily salt limit, 6 g | 2.4 g | 103 mmol |
| 1 litre of 0.9% sodium chloride | 3.54 g | 154 mmol |
One charge, one number — and a unit that is not what it looks like
Sodium is reported in mmol/L in the United Kingdom and much of the world and in mEq/L in the United States, and those two figures are the same number. A milliequivalent counts charge and a millimole counts particles; sodium carries a single positive charge, so one millimole is one milliequivalent. A sodium of 140 mmol/L is 140 mEq/L, and no conversion should ever be applied between them. The mg/dL column is a different matter, converting by 10 ÷ 22.99, the atomic mass, or 0.4350 mmol/L per mg/dL.
No routine clinical laboratory reports serum sodium in mg/dL, so that unit is here for the places milligrams of sodium genuinely appear: food labelling, dietary advice, urinary collections quoted in milligrams, and older literature. One gram of salt contains 393 mg of sodium, which is 17.1 mmol, and a litre of 0.9% sodium chloride carries 154 mmol. Keeping salt and sodium apart matters, because the two differ by a factor of 2.54 and quoting one as the other is the commonest error in dietary arithmetic.
Clinically, the sodium concentration is a statement about water rather than about salt. Hyponatraemia usually means too much water relative to solute rather than a depleted sodium store, which is why the assessment turns on volume status, urine osmolality and urine sodium rather than the serum figure alone. Before any of that, exclude a spurious result: severe hypertriglyceridaemia or a paraprotein produces pseudohyponatraemia on indirect ion-selective electrodes, and marked hyperglycaemia lowers sodium by drawing water out of cells.
The rate of correction then matters more than the starting value. In chronic hyponatraemia, raising sodium by more than about 8 to 10 mmol/L in twenty-four hours risks osmotic demyelination, and the risk is highest in exactly the patients who look most correctable — those with alcohol dependence, malnutrition, hypokalaemia or advanced liver disease. Overcorrection can be relowered with desmopressin and dextrose if it is caught early, so sodium should be rechecked every few hours during active treatment.
Frequently asked questions
Is mmol/L the same as mEq/L for sodium?
Yes, exactly. Sodium is monovalent, so one millimole carries one milliequivalent of charge and the two numbers are identical. A sodium of 140 mmol/L is 140 mEq/L. No conversion is needed, and applying one introduces an error.
How do I convert sodium from mg/dL to mmol/L?
Multiply by 0.435, which is 10 divided by the atomic mass of sodium, 22.99. A value of 322 mg/dL is 140.1 mmol/L. To go the other way, multiply the mmol/L figure by 2.299.
Why would sodium ever be reported in mg/dL?
Serum sodium is not, in routine practice. Milligrams appear on food labels, in dietary advice and in some urinary collections. One gram of salt contains 393 mg of sodium, or 17.1 mmol, so salt and sodium differ by a factor of 2.54.
What is a normal serum sodium?
Around 135 to 145 mmol/L in adults, which is 135 to 145 mEq/L. Intervals differ by a millimole or two between laboratories, so check the range printed on your own report before calling a borderline value abnormal.
Why is my sodium low when I am not short of salt?
Because the sodium concentration reflects water balance, not sodium stores. Excess water from SIADH, heart failure, cirrhosis or excessive intake dilutes it. High glucose and, on some analysers, severe hyperlipidaemia or a paraprotein also lower the measured value.
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References
- Spasovski G, Vanholder R, Allolio B, et al. Clinical practice guideline on diagnosis and treatment of hyponatraemia. Eur J Endocrinol. 2014;170(3):G1–G47.
- Verbalis JG, Goldsmith SR, Greenberg A, et al. Diagnosis, evaluation, and treatment of hyponatremia: expert panel recommendations. Am J Med. 2013;126(10 Suppl 1):S1–S42.
- Rifai N, Horvath AR, Wittwer CT, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 6th ed. Elsevier; 2018.