Calculate urine calcium, urine creatinine, or the Ca/Cr ratio from two values, with mg/dL, mmol/L, µmol/L, mg/mg, mg/g, and mmol/mmol conversions.
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Urine Ca/Cr Ratio Formula
The urine calcium-to-creatinine ratio compares the calcium concentration in a urine sample with the creatinine concentration from the same urine sample. The calculator uses mg/dL internally for calcium and creatinine, then displays the ratio as either mg/mg or mmol/mmol.
- Ca/Cr = urine calcium-to-creatinine ratio in mg/mg
- Ca = urine calcium concentration in mg/dL
- Cr = urine creatinine concentration in mg/dL
If you enter the ratio and creatinine, the calculator rearranges the formula to solve for urine calcium:
If you enter the ratio and calcium, the calculator rearranges the formula to solve for urine creatinine:
For mmol/mmol ratio reporting, the calculator converts between mass ratio and molar ratio using the molecular weights of calcium and creatinine:
- 40.08 = molecular weight of calcium in g/mol
- 113.12 = molecular weight of creatinine in g/mol
The calculator has three functions: it can calculate the Ca/Cr ratio from urine calcium and urine creatinine, calculate urine calcium from a known ratio and creatinine, or calculate urine creatinine from a known ratio and calcium. The calcium and creatinine values must come from urine, not serum, and should be from the same sample.
Common Unit Conversions for Urine Ca/Cr Calculations
| Measurement | Entered unit | Conversion to calculator base unit |
|---|---|---|
| Urine calcium | mg/dL | No conversion |
| Urine calcium | mmol/L | mg/dL = mmol/L × 4.008 |
| Urine creatinine | mg/dL | No conversion |
| Urine creatinine | mmol/L | mg/dL = mmol/L × 11.312 |
| Urine creatinine | µmol/L | mg/dL = µmol/L ÷ 88.3465 |
General Ca/Cr Ratio Reference Notes
| Result pattern | What to check |
|---|---|
| Unexpectedly high Ca/Cr ratio | Confirm the calcium and creatinine are both urine results, check units, and compare with the lab’s age-specific reference range. |
| Very low urine creatinine | The urine may be dilute, or the wrong unit may have been entered. |
| Creatinine reported in µmol/L | Double-check that the value is urine creatinine. Serum creatinine is often reported in µmol/L and should not be used here. |
Example Urine Ca/Cr Ratio Calculations
Example 1: Calculate Ca/Cr ratio in mg/mg
You have urine calcium of 12 mg/dL and urine creatinine of 80 mg/dL.
The urine Ca/Cr ratio is 0.15 mg/mg.
Example 2: Calculate urine calcium from a known ratio
You have a Ca/Cr ratio of 0.20 mg/mg and urine creatinine of 100 mg/dL.
The urine calcium concentration is 20 mg/dL.
FAQ
What samples should I use for a urine Ca/Cr ratio?
Use urine calcium and urine creatinine results from the same urine sample. Do not mix a urine calcium result with a serum creatinine result. Serum creatinine values are not valid for this ratio.
What is the difference between mg/mg and mmol/mmol?
mg/mg is a mass ratio, while mmol/mmol is a molar ratio. They are not numerically the same because calcium and creatinine have different molecular weights. The calculator converts between them using 40.08 g/mol for calcium and 113.12 g/mol for creatinine.
Can I diagnose hypercalciuria from the Ca/Cr ratio alone?
No. The urine Ca/Cr ratio is a screening or comparison value, and interpretation depends on age, collection timing, diet, hydration, and the lab’s reference range. A clinician may use it with symptoms, history, blood tests, or a 24-hour urine collection.
