Urine Sodium Unit Converter
Urine Sodium Unit Converter
A urine sodium answers a different question from a serum sodium: not how much sodium is in the body, but what the kidney is doing about it. Convert mmol/L, mEq/L and mg/dL.
Urine Sodium converter
Monovalent — mmol/L = mEq/LSpot urine sodium 15 mmol/L, in oliguric acute kidney injury, no diuretic given
Formula and conversion factors
mg/dL = mmol/L ÷ 0.434976
mEq/L = mmol/L (sodium is monovalent)
mmol/24 h = concentration in mmol/L × collection volume in litres
- 0.434976
- derived from the atomic weight of sodium, 22.98977 — the same factor the serum sodium page uses, because it is the same ion
- mmol/L = mEq/L
- sodium carries one charge, so the two units are numerically identical
- volume
- the step this converter cannot take for you: a concentration becomes a 24-hour excretion only when multiplied by the measured collection volume
Worked example
Spot urine sodium 15 mmol/L, in oliguric acute kidney injury, no diuretic given
15.0 mmol/L — and 15.0 mEq/L, the same number
15 ÷ 0.434976 = 34.5 mg/dL = 345 mg/L
Below 20 mmol/L, which the Merck Manual gives as the pre-renal pattern
In a 1.8 L collection this would be 27 mmol of sodium in 24 hours — the volume, not the converter, supplies that
Spot urine sodium converted
| mmol/L (mEq/L) | mg/dL | mg/L |
|---|---|---|
| 10.0 | 23.0 | 230 |
| 20.0 | 46.0 | 460 |
| 40.0 | 92.0 | 920 |
| 100.0 | 229.9 | 2,299 |
| 200.0 | 459.8 | 4,598 |
What a urine sodium can and cannot be read against
| Source and basis | Figure | Unit |
|---|---|---|
| Mayo NAU, 24-hour, adults 18 and over | 22 – 328 | mmol/24 h |
| ARUP ULYTE, 24-hour collection | 51 – 286 | mmol/day |
| Merck Manual, spot, prerenal azotaemia | Below 20 | mmol/L |
| Merck Manual, spot, acute tubular necrosis | Above 40 | mmol/L |
| Mayo, random urine sodium (RNAUR) | No established reference values | — |
| ARUP, random urine electrolytes (ULYTE) | Not established for random urines | — |
What a urine sodium is actually telling you
A serum sodium and a urine sodium answer different questions. The serum value is a statement about tonicity — how much water there is relative to solute — and it is interpreted against a reference interval. The urine value is a statement about what the kidney is doing: whether it is holding sodium back because perfusion is poor, or letting it go because intake is high or the tubule is injured. That is why it has no reference interval worth the name, and why both Mayo and ARUP print exactly that against their random-urine tests. If you want the blood side of the pair, use the serum sodium unit converter.
The arithmetic is the easy part. Sodium is monovalent, so mmol/L and mEq/L are the same number, and mg/dL is mmol/L divided by 0.434976 — a factor derived from the atomic weight 22.98977, identical to the one used for serum sodium because the molecule has not changed. A urine sodium is not reported in mass units anywhere in routine practice; the column exists because dietary sodium and salt labelling are, and because older papers used it.
The trap on this page is the difference between a concentration and an excretion. A spot urine sodium of 15 mmol/L in a volume-depleted patient and the same 15 mmol/L in a patient drinking four litres a day mean opposite things, because the second is excreting four times as much sodium. Turning a concentration into a 24-hour excretion needs the collection volume, which no converter can supply: 15 mmol/L is 15 mmol in a litre and 37.5 mmol in 2.5 litres. Correct for dilution instead — divide by the creatinine on the same sample, or calculate the fractional excretion of sodium, which is what the pre-renal question actually turns on.
Two more cautions. A diuretic makes the kidney excrete sodium whatever the volume status, so a urine sodium taken within a day or so of a loop or thiazide dose classifies nothing. And in heart failure and in cirrhosis the urine sodium is often under 10 mmol/L despite obvious oedema, because the kidney is responding to a low effective arterial volume rather than to total body sodium — the number is correct and the intuition is wrong.
Frequently asked questions
Is a urine sodium in mmol/L the same as mEq/L?
Yes. Sodium carries a single positive charge, so one millimole is one milliequivalent and a report of 15 mmol/L and one of 15 mEq/L mean exactly the same thing. US laboratories tend to print mEq/L and the rest of the world mmol/L.
How do I convert a urine sodium to mg/dL?
Divide the mmol/L figure by 0.434976, or multiply by 2.299 to get mg/dL directly. The factor comes from sodium’s atomic weight of 22.98977. Mass units are not used on urine reports — they belong to dietary work.
What is a normal urine sodium?
For a spot sample there is no such figure, and that is the honest answer: Mayo Clinic Laboratories records “no established reference values” for a random urine sodium and ARUP states that intervals are not established for random urines. On a 24-hour collection Mayo gives 22 to 328 mmol/24 h and ARUP 51 to 286 mmol/day, and the width of both reflects diet.
Can I turn a spot urine sodium into a 24-hour sodium excretion?
Not from the concentration alone. Excretion is concentration multiplied by volume, so 15 mmol/L is 15 mmol over a litre but 37.5 mmol over 2.5 litres. Either collect for 24 hours and record the volume, or normalise the spot sample to its creatinine.
Why is the urine sodium low in heart failure and cirrhosis?
Because the kidney responds to effective arterial blood volume, not to total body sodium. In both conditions that volume is sensed as low, so sodium is retained avidly and the urine sodium falls below 10 to 20 mmol/L even while the patient is visibly overloaded.
Related calculators
References
- Mayo Clinic Laboratories. Sodium, 24 hour, urine (NAU) — reference values. Test catalogue, test ID 610734; 2026.
- Mayo Clinic Laboratories. Sodium, random, urine (RNAUR) — reference values and interpretation. Test catalogue, test ID 610785; 2026.
- ARUP Laboratories. Electrolytes, urine (ULYTE) — reference intervals for sodium, potassium and chloride per 24 hours. Laboratory Test Directory 0020498; 2026.
- Merck Manual Professional Edition. Laboratory findings distinguishing acute tubular necrosis from prerenal azotemia. Revised 2025.
- Kamel KS, Halperin ML. Use of urine electrolytes and urine osmolality in the clinical diagnosis of fluid, electrolytes, and acid-base disorders. Kidney Int Rep. 2021;6(5):1211–1224.
Not medical advice. For healthcare professionals and education. Reference intervals vary by laboratory and assay — always use your own laboratory's. Never base a dose or a treatment decision on this page alone. Full disclaimer at calcengines.com/disclaimer/