BUN Creatinine Ratio Calculator

Calculate the blood urea nitrogen (BUN) to creatinine ratio from routine kidney function results. Enter BUN in mg/dL (or urea in mmol/L) and creatinine in mg/dL or µmol/L.

Enter your values above — the result appears instantly. Nothing you type leaves your device.
Medical disclaimer: This calculator is intended for educational and informational purposes and does not replace professional medical advice, diagnosis, laboratory interpretation, or treatment. Laboratory methods and reference intervals vary. Always consult a qualified healthcare professional about your results.

How the BUN/Creatinine Ratio Calculator works

Blood urea nitrogen (BUN) and creatinine are both waste products cleared by the kidneys, but they are affected by different factors. BUN is influenced by protein intake, protein breakdown, hydration and liver function, while creatinine mainly reflects muscle mass and kidney filtration. Comparing the two as a ratio can give clinicians additional context when reviewing kidney function results.

Required inputs

  • BUN in mg/dL — or serum urea in mmol/L (converted: urea mmol/L × 2.8 = BUN mg/dL)
  • Serum creatinine in mg/dL or µmol/L (µmol/L ÷ 88.4 = mg/dL)

Note: the ratio is calculated in conventional units (mg/dL ÷ mg/dL). A urea/creatinine ratio calculated directly in SI units is on a different scale.

Formula used

BUN : Creatinine ratio = BUN (mg/dL) ÷ serum creatinine (mg/dL)

Worked example

BUN 15 mg/dL and creatinine 1.0 mg/dL:

  • Ratio = 15 ÷ 1.0 = 15 : 1

Using SI units — urea 5.4 mmol/L and creatinine 88 µmol/L: BUN = 5.4 × 2.8 = 15.1 mg/dL; creatinine = 88 ÷ 88.4 = 1.0 mg/dL; ratio ≈ 15 : 1.

Interpreting the result

A ratio of roughly 10:1 to 20:1 is commonly cited as the usual range, although laboratories and textbooks vary.

  • A higher ratio may be associated with reduced kidney blood flow (for example dehydration or heart failure), gastrointestinal bleeding, high protein intake, corticosteroid use, or urinary tract obstruction.
  • A lower ratio may be associated with low protein intake, liver disease, or low muscle mass factors affecting creatinine.

Because many unrelated factors change the ratio, the result alone cannot diagnose dehydration, kidney disease, bleeding or any other condition.

Limitations

  • Both values must come from the same blood sample and be entered in the correct units.
  • The ratio can look normal even when both BUN and creatinine are high.
  • Reference intervals vary by laboratory, age and population.
  • Interpret together with eGFR, history, examination and other tests.

Frequently asked questions

It is the blood urea nitrogen value divided by the serum creatinine value, both in mg/dL. It gives context about factors that affect BUN differently from creatinine.

A range of about 10:1 to 20:1 is commonly cited, but reference intervals vary between laboratories. Check the range printed on your lab report.

Yes. Select "Urea mmol/L" and the calculator converts it to BUN in mg/dL (× 2.8) before calculating the conventional ratio.

Not necessarily. Dehydration is one possible association, but diet, medicines, bleeding and other conditions can also raise the ratio. Only a clinician can interpret it in context.
Medical disclaimer: This calculator is intended for educational and informational purposes and does not replace professional medical advice, diagnosis, laboratory interpretation, or treatment. Laboratory methods and reference intervals vary. Always consult a qualified healthcare professional about your results.