Urine Calcium-Creatinine Ratio Calculator
Urine Calcium-Creatinine Ratio Calculator
Calculate the spot urine calcium-creatinine ratio in mmol/mmol with the mg/mg equivalent stated at every threshold, against age-specific limits — the paediatric upper limit at six months is nearly four times the adult one.
Urine Calcium-Creatinine Ratio
Calcium ÷ creatinineUrine calcium 2.4 mmol/L, urine creatinine 6 mmol/L, adult
Formula
Ratio (mmol/mmol) = ratio (mg/mg) × 2.82
Adult upper limit: 0.2 mg/mg = 0.56 mmol/mmol
- × 2.82
- the mg/mg to mmol/mmol factor, and the number this page exists to pin down. It is the ratio of the molecular masses, 113.12 for creatinine over 40.078 for calcium. The reciprocal, for going the other way, is 0.354. A ratio of 0.2 quoted without units is either normal (mg/mg) or reassuringly low (mmol/mmol), and the two cannot be told apart from the number
- mg/dL to mmol/L
- calcium: divide mg/dL by 4.008. Creatinine: multiply mg/dL by 0.0884. Both inputs on this page are mmol/L
- age
- the upper limit falls from about 2.3 mmol/mmol under six months to about 0.7 mmol/mmol by seven years, largely because creatinine output rises with muscle mass. This is why the age group is an input and not a footnote
- 24-hour confirmation
- hypercalciuria in adults is over 275 mg/day in men, over 250 mg/day in women, or over 4 mg/kg/day; in children, over 4 mg/kg/day (0.1 mmol/kg/day). The spot ratio screens, the collection confirms
- what this is not
- the calcium-creatinine clearance ratio. That test, used to separate familial hypocalciuric hypercalcaemia from primary hyperparathyroidism, needs paired serum and urine calcium and creatinine. A spot calcium-creatinine ratio is not a substitute for it
Worked example
Urine calcium 2.4 mmol/L, urine creatinine 6 mmol/L, adult
2.4 ÷ 6 = 0.40 mmol/mmol
0.40 ÷ 2.82 = 0.14 mg/mg
Below 0.6 mmol/mmol (0.21 mg/mg) → within the adult reference range
The same 0.40 mmol/mmol in a four-month-old infant would be well within a limit of about 2.3 — the number is meaningless until the age is attached
Upper limit of normal by age, both units
| Age | mg/mg | mmol/mmol |
|---|---|---|
| 1 to under 12 months | 0.81 | 2.3 |
| 12 to under 24 months | 0.56 | 1.6 |
| 2 to under 3 years | 0.50 | 1.4 |
| 3 to under 5 years | 0.41 | 1.2 |
| 5 to under 7 years | 0.30 | 0.85 |
| 7 to under 18 years | 0.25 | 0.70 |
| Adult | 0.20 to 0.27 | 0.56 to 0.76 |
Causes of hypercalciuria, grouped by what to check
| Serum calcium | Group | Examples |
|---|---|---|
| Raised | Calcium coming from bone or gut | Primary hyperparathyroidism, malignancy, sarcoidosis and other granulomatous disease, vitamin D excess, immobilisation, thyrotoxicosis, Paget disease |
| Normal | Idiopathic hypercalciuria | The commonest finding in adult and paediatric stone formers, often familial. Absorptive, resorptive and renal-leak subtypes are described but rarely separated in practice |
| Normal or low | Renal tubular | Distal renal tubular acidosis, Dent disease, Bartter syndrome, familial hypomagnesaemia with hypercalciuria and nephrocalcinosis, medullary sponge kidney |
| Normal | Drug and diet | Loop diuretics, acetazolamide, topiramate, high dietary sodium, ketogenic diet, excess vitamin D or calcium supplementation |
A ratio that means nothing until you attach the units and the age
The spot urine calcium-creatinine ratio screens for hypercalciuria without a timed collection, which is why it dominates paediatric practice and why it is used to monitor adult stone formers between 24-hour urines. Dividing by creatinine is what makes a spot sample interpretable: a urine concentration on its own says as much about how much the patient drank as about what the kidney did. Two things have to travel with the number, though, and both are routinely dropped. The first is the units. A ratio of 0.2 in mg/mg is the conventional adult upper limit; the same 0.2 in mmol/mmol is comfortably normal, because mmol/mmol is 2.82 times mg/mg — the ratio of creatinine’s molecular mass to calcium’s, 113.1 over 40.1. Nothing in the bare number distinguishes the two, so this page prints both at every threshold.
The second is age, and the dependence is steep. The upper limit of normal is around 0.81 mg/mg (2.3 mmol/mmol) in the first year of life, about 0.50 mg/mg (1.4 mmol/mmol) at two to three years, and has reached the adult 0.25 mg/mg (0.70 mmol/mmol) by around seven. Most of that fall is the denominator: creatinine excretion rises with muscle mass, so the same calcium output divided by a growing creatinine gives a falling ratio. Reading an infant’s ratio against the adult limit is the classic false positive on this test, and it generates unnecessary imaging and unnecessary anxiety.
In children, hypercalciuria is the commonest metabolic abnormality found in those investigated for unexplained haematuria or a first stone, and it is frequently idiopathic and familial. In adults, it is the commonest metabolic abnormality in calcium stone disease, and it is the abnormality most amenable to treatment: fluid, dietary sodium restriction, normal rather than low dietary calcium, and a thiazide where diet is not enough. In both groups the spot ratio screens and a 24-hour collection confirms — over 275 mg/day in men, 250 mg/day in women, or 4 mg/kg/day at any age — because the spot ratio moves with the preceding meal and with the time of day, and a fasting second-void sample is the most comparable one to repeat.
One boundary is worth marking clearly. This is not the calcium-creatinine clearance ratio. That test, which helps separate familial hypocalciuric hypercalcaemia from primary hyperparathyroidism, needs paired serum and urine calcium and creatinine and answers a question about fractional reabsorption, not about calcium load. A low spot calcium-creatinine ratio in a hypercalcaemic patient is suggestive and no more; the clearance ratio is the calculation that discipline requires. This calculator supports a clinician’s assessment and does not replace it.
Frequently asked questions
What is a normal urine calcium-creatinine ratio in adults?
Below about 0.2 mg/mg, which is 0.56 mmol/mmol, with 0.18 mg/mg (0.51 mmol/mmol) suggested as optimal for a stone former. Some laboratories publish an upper reference limit as high as 0.27 mg/mg (0.76 mmol/mmol), so check your own report’s interval before acting on a borderline result.
How do I convert a calcium-creatinine ratio between mg/mg and mmol/mmol?
Multiply mg/mg by 2.82 to get mmol/mmol, and multiply mmol/mmol by 0.354 to go back. The factor is the ratio of the molecular masses, 113.1 for creatinine over 40.1 for calcium. So 0.2 mg/mg is 0.56 mmol/mmol, and 0.6 mmol/mmol is 0.21 mg/mg.
Why is the normal urine calcium-creatinine ratio so much higher in babies?
Mostly because of the denominator. Creatinine excretion tracks muscle mass, which is small in infancy, so the same calcium output divided by a smaller creatinine gives a higher ratio. The upper limit is about 0.81 mg/mg (2.3 mmol/mmol) in the first year and falls to the adult figure by around seven years.
Does a high spot ratio confirm hypercalciuria?
No. It screens for it. The spot ratio varies with the preceding meal and the time of day, so confirm a raised result on a fasting second-void repeat and, where practical, with a 24-hour urinary calcium: over 275 mg/day in men, over 250 mg/day in women, or over 4 mg/kg/day at any age.
Can this ratio diagnose familial hypocalciuric hypercalcaemia?
Not on its own. That distinction uses the calcium-creatinine clearance ratio, which needs paired serum and urine calcium and creatinine; values below about 0.01 favour familial hypocalciuric hypercalcaemia and above 0.02 favour primary hyperparathyroidism. A low spot calcium-creatinine ratio is suggestive but is not the same calculation.
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References
- Sorokin I, Mamoulakis C, Miyazawa K, et al. Epidemiology of stone disease across the world. World J Urol. 2017;35(9):1301–1320.
- Reusz GS, Dobos M, Byrd D, et al. Urinary calcium and oxalate excretion in children. Pediatr Nephrol. 1995;9(1):39–44.
- Kaur M, Mehta B. Hypercalciuria. In: StatPearls. Treasure Island, FL: StatPearls Publishing; 2024.
- Mayo Clinic Laboratories. Calcium/creatinine ratio, random, urine — age-specific reference values. Test catalogue, 2025.
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.