BUN/Creatinine Ratio Calculator
BUN (blood urea nitrogen) and creatinine both appear on a standard metabolic panel, and both relate to kidney function — but reading them as a ratio adds context that neither number gives alone. The BUN/creatinine ratio is one of the oldest pattern-recognition tools in clinical chemistry: it helps separate a hydration-or-flow story from a kidney story.
From your metabolic panel (CMP or BMP)
From the same panel
Enter your values above to see your results.
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The formula
BUN/Creatinine ratio = BUN (mg/dL) ÷ creatinine (mg/dL). Both values come from the same standard metabolic panel — no extra test needed. The ratio is unitless, so it works the same whether your report says 14/1.0 or shows the numbers side by side.
Why a ratio instead of two numbers?
BUN and creatinine are both cleared by the kidneys, but BUN is also influenced by hydration, protein intake, and gut absorption, while creatinine tracks muscle mass and filtration more tightly. When both rise together, the ratio stays near normal (suggesting a filtration issue); when BUN climbs alone, the ratio rises above 20:1 (the classic dehydration or 'prerenal' pattern). The ratio is a context tool, not a standalone answer.
Limitations
The 10:1–20:1 range is a textbook convention, not a formal guideline threshold, and individual baselines vary with muscle mass, diet, age, and medications. Very muscular people run higher creatinine (lower ratio); low muscle mass does the opposite. A screening signal, not a diagnosis — interpretation belongs with a practitioner who has your full panel and history.
Frequently asked questions
How do I calculate my BUN/creatinine ratio?
Divide your BUN by your creatinine, both in mg/dL from the same metabolic panel. Example: BUN 14 mg/dL and creatinine 1.0 mg/dL → ratio 14. The calculator above does this in one step and reads the result against textbook reference bands.
What is a normal BUN/creatinine ratio?
The classic textbook range is 10:1 to 20:1 for adults. It's a general convention rather than an official guideline cutoff — diet, muscle mass, and hydration all shift it, so your trend over time and your lab's own reference range are more informative than any single reading.
What does a BUN/creatinine ratio above 20 mean?
In textbook pattern-reading, a ratio above 20:1 suggests BUN is rising faster than creatinine — classically from dehydration, reduced blood flow to the kidneys, high protein intake, or GI bleeding. It's a screening signal, not a diagnosis: the absolute BUN and creatinine values and your clinical context determine what it actually means.
Is this the same as eGFR?
No. eGFR estimates filtration rate from creatinine (plus age and sex) and is the standard kidney-function number on most reports. The BUN/creatinine ratio is an older pattern tool that adds hydration and context information. They complement each other — most panels report both BUN and creatinine, so you can compute both.
Is a BUN/creatinine ratio a diagnosis of kidney disease?
No. It's a screening signal computed from two routine labs. Kidney assessment uses the full picture — eGFR, urinalysis, symptoms, blood pressure, and history. Always review your results with a qualified healthcare professional.
Sources
- Standard clinical chemistry teaching (BUN/creatinine ratio 10:1–20:1 adult convention) — Tietz Textbook of Laboratory Medicine.
- Hosten AO. BUN and Creatinine. In: Clinical Methods: The History, Physical, and Laboratory Examinations (NCBI Bookshelf), 1990.
This calculator is for informational purposes only and is not medical advice, diagnosis, or treatment. Reference ranges are general population guidelines — always discuss your lab results with a qualified healthcare professional.