Urine Calcium Unit Converter
Urine Calcium Unit Converter
Urine calcium is a stone and bone test, and the number that counts is the 24-hour excretion. Convert mg/dL, mg/L, mmol/L and mEq/L, with the mg/24 h multiplier.
Urine Calcium converter
Divalent — mEq/L = 2 × mmol/LUrine calcium 15 mg/dL on a spot sample, with a 24-hour collection pending
Formula and conversion factors
mmol/24 h = mg/24 h × 0.0249513
mEq = 2 × mmol (calcium is divalent)
mg/24 h = concentration in mg/L × collection volume in litres
- 0.249513
- concentration factor, from the atomic weight of calcium, 40.078 — the same number the serum calcium page uses
- 0.0249513
- excretion factor, for mg/24 h to mmol/24 h. Ten times smaller than the concentration factor, because that one also converts decilitres to litres
- divalent
- calcium carries two charges, so mEq is twice mmol in either family
Worked example
Urine calcium 15 mg/dL on a spot sample, with a 24-hour collection pending
15 × 0.249513 = 3.74 mmol/L
= 7.49 mEq/L, because calcium is divalent
A concentration, not an excretion: the same 15 mg/dL over a 1.6 L collection is 240 mg/24 h, and over a 2.6 L collection 390 mg/24 h
240 mg/24 h is below Mayo's male cut-off of 250 and above its female cut-off of 200 — one result, two verdicts, depending on which limit applies
Calcium: the two multipliers, and why they differ
| Conversion | Multiplier | Worked |
|---|---|---|
| mg/dL to mmol/L (a concentration) | 0.249513 | 15 mg/dL = 3.74 mmol/L |
| mg/24 h to mmol/24 h (an excretion) | 0.0249513 | 250 mg/24 h = 6.24 mmol/24 h |
| mmol/L to mEq/L | 2 | Calcium is divalent |
| mg/dL to mg/L | 10 | 15 mg/dL = 150 mg/L |
24-hour urine calcium: what the sources actually say
| Source and basis | Figure | Unit |
|---|---|---|
| Mayo CALU, males, stone-risk cut-off | Below 250 | mg/24 h |
| Mayo CALU, females, stone-risk cut-off | Below 200 | mg/24 h |
| Ryan and Ing, oestrogen-replete women | Above 250 | mg/day |
| Ryan and Ing, oestrogen-deprived women | Above 300 | mg/day |
| EAU 2026, reference value, risk assessed above it | Below 5.0 | mmol/day |
| EAU 2026, needs attention above this | Above 8.0 | mmol/day |
| ARUP, average calcium diet | 100 – 250 | mg/day |
| ARUP, low calcium diet | 50 – 150 | mg/day |
| ARUP, calcium-free diet | 5 – 40 | mg/day |
A stone and bone number, not a defended one
A serum calcium is tightly defended: parathyroid hormone and vitamin D hold it inside a narrow interval, and a value outside that interval is itself the abnormality. A urine calcium is the opposite kind of number. It is the amount the kidney is letting go, it varies with what was eaten, and it is read against risk thresholds rather than a reference interval. For the blood side of the pair use the serum calcium unit converter.
The 24-hour collection is the standard test, and this is where the units trap people. A concentration in mg/dL becomes mmol/L by multiplying by 0.249513; a daily excretion in mg/24 h becomes mmol/24 h by multiplying by 0.0249513. Both come from the atomic weight of 40.078, but they differ by a factor of ten, and using one where the other belongs turns 250 mg/24 h into 62 mmol/24 h instead of 6.2 — an error that still looks like arithmetic. Calcium is also divalent, so mEq is twice mmol.
The published thresholds do not agree, and the disagreement matters clinically. Mayo reports above 250 mg/24 h in men and above 200 mg/24 h in women as the stone-risk cut-offs, noting that these are clinical limits rather than a reference-range study. The bone literature uses higher numbers: Ryan and Ing define hypercalciuria as above 250 mg/day in oestrogen-replete women and above 300 mg/day in oestrogen-deprived women. The EAU urolithiasis guideline works in millimoles, treating 5.0 mmol/day as the reference value and above 8.0 mmol/day as needing attention. A result of 240 mg/24 h is therefore normal by one source and hypercalciuric by another, which is a reason to say which source you are using rather than to pick one silently. The 24-hour urine stone-risk interpreter reads a full panel against the EAU limits.
Two practical points. ARUP publishes its 24-hour calcium interval stratified by diet — 5 to 40 mg/day on a calcium-free diet, 100 to 250 mg/day on an average one — which is the clearest statement anywhere that this test measures intake as much as handling. And on a spot sample the reported result is normally a calcium-to-creatinine ratio rather than a concentration, because concentration alone is a statement about hydration; see the urine calcium-creatinine ratio calculator.
Frequently asked questions
How do I convert urine calcium from mg/24 h to mmol/24 h?
Multiply by 0.0249513, which is one divided by the atomic weight of calcium, 40.078. A 24-hour calcium of 250 mg is 6.24 mmol. Do not use the mg/dL to mmol/L factor of 0.249513 here — it is ten times too large.
Why are there two different calcium conversion factors on this page?
Because one converts a concentration and the other an amount. Both divide by the atomic weight, but mg/dL to mmol/L also has to turn a per-decilitre figure into a per-litre one, which multiplies in a factor of ten. A per-24-hour figure has no volume in it at all, so mg/24 h to mmol/24 h is simply one over the atomic weight.
What counts as hypercalciuria on a 24-hour urine?
It depends on the source. Mayo uses above 250 mg/24 h for men and above 200 mg/24 h for women; Ryan and Ing use above 250 mg/day in oestrogen-replete and above 300 mg/day in oestrogen-deprived women; the EAU guideline uses above 8.0 mmol/day, about 321 mg. Quote the threshold you are using.
Can a spot urine calcium be used instead of a 24-hour collection?
Only as a calcium-to-creatinine ratio, which corrects for how dilute the sample is. A bare concentration mostly reflects hydration. Mayo reports its random urine calcium as a ratio to creatinine for exactly that reason.
Is urine calcium in mEq the same as mmol?
No — calcium is divalent, so one millimole is two milliequivalents. A urine calcium of 3.74 mmol/L is 7.48 mEq/L. Mixing the two is a twofold error in whichever direction it is made.
Related calculators
References
- Mayo Clinic Laboratories. Calcium, 24 hour, urine (CALU) — reference values. Test catalogue, test ID 610595; 2026.
- Mayo Clinic Laboratories. Calcium, random, urine (CALC5) — age-specific calcium/creatinine reference values. Test catalogue, test ID 610591; 2026.
- ARUP Laboratories. Calculi risk assessment, urine — diet-stratified 24-hour urine calcium reference intervals. Laboratory Test Directory 2008708; 2026.
- European Association of Urology. EAU Guidelines on Urolithiasis, chapter 4: Metabolic evaluation and recurrence prevention, Table 4.2. EAU Guidelines Office, Arnhem; 2026 edition.
- Ryan LE, Ing SW. Idiopathic hypercalciuria: can we prevent stones and protect bones? Cleve Clin J Med. 2018;85(1):47–54.
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/