Calculate urine calcium, creatinine, or Ca/Cr ratio from two values, converting between mg/dL, mmol/L, µmol/L, and mg/mg or mmol/mmol.

Urine Ca/Cr Ratio Calculator

Note: Use urine (not blood/serum) results from the same sample.

This tool converts your entries to consistent units before calculating. If you change a unit dropdown after typing a value, update the number to match the unit shown on your lab report.

Enter any 2 values to calculate the missing variable

Unit tip: Most urine creatinine results are reported in mg/dL or mmol/L. µmol/L is uncommon for urine—double-check your report to avoid accidentally entering serum creatinine.

Common reporting formats include mg/mg (mass ratio) and mmol/mmol (molar ratio). Select the unit you want for the ratio field.

Medical disclaimer: Educational use only. Not medical advice or a diagnosis. Do not start, stop, or change medications or supplements (including calcium/vitamin D) based on this tool. Use your lab’s reference range; interpretation varies by age (especially children), pregnancy status, hydration, diet, and lab methods. Discuss abnormal results with a licensed clinician.

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 = Ca / Cr
  • 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:

Ca = Ca/Cr * Cr

If you enter the ratio and calcium, the calculator rearranges the formula to solve for urine creatinine:

Cr = Ca / Ca/Cr

For mmol/mmol ratio reporting, the calculator converts between mass ratio and molar ratio using the molecular weights of calcium and creatinine:

Ca/Cr_mg/mg = Ca/Cr_mmol/mmol * (40.08 / 113.12)
Ca/Cr_mmol/mmol = Ca/Cr_mg/mg * (113.12 / 40.08)
  • 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.

Ca/Cr = 12 / 80 = 0.15 mg/mg

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.

Ca = 0.20 * 100 = 20 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.