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Blood Test Tracker

BUN to creatinine ratio calculator

A calculated comparison of your BUN with your creatinine that clinicians use as one clue to why a kidney-related number is high or low. Type your results in the units on your report and it works out BUN/Cr Ratio as you type, in your browser.

AI-verified against cited sources. Awaiting expert reviewLast reviewed 2026-10-03Kidneys

Type your results above, or fill in the example, to see BUN/Cr Ratio.

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Educational information, not medical advice. Blood Test Tracker doesn’t diagnose or treat, and it doesn’t replace your clinician. Talk with your clinician before changing medications, supplements or care.

How it’s worked out

The formula

BUN (mg/dL) ÷ serum creatinine (mg/dL). Both values must be in mg/dL and from the same blood draw.

A worked example

Example numbers, not anyone’s real results, run through the same code as the calculator above.

Example inputs and the result
BUN18 mg/dL
Creatinine0.9 mg/dL
BUN/Cr Ratio20.0 ratio

What BUN/Cr Ratio tells you

The ratio is your BUN divided by your creatinine, with both measured in mg/dL. Many metabolic panels calculate it for you. BUN and creatinine are affected by different things. BUN moves with hydration and protein intake, and creatinine moves with muscle mass. So the ratio can offer a clue about why one of them is off. It is not a separate test and only means something next to both of its numbers.

A clinician may look at the ratio when BUN or creatinine is out of range. A higher ratio is seen with dehydration, bleeding in the digestive tract and a lot of protein breakdown. A lower ratio is seen with low protein intake, liver disease and some kidney problems. The ratio alone cannot show what is going on, and it does not tell you how well your kidneys work. It can sit in the usual span even when BUN and creatinine are both high.

Read the full page on BUN/Cr Ratio, with what a high or low result can mean.

Usual ranges

The ranges the result above is placed on. Your own lab’s printed range comes first if it gives one.

  • Men, 18–599–20 ratio

    Source: Labcorp

  • Women, 18–599–23 ratio

    Source: Labcorp

  • 13–1710–22 ratio

    Source: Labcorp

  • Men, 6–1214–34 ratio

    Source: Labcorp

  • Women, 6–1213–32 ratio

    Source: Labcorp

  • Men, 2–519–51 ratio

    Source: Labcorp

  • Women, 2–519–49 ratio

    Source: Labcorp

Sources

The equation

  1. LOINC 3097-3: Urea nitrogen/Creatinine [Mass Ratio] in Serum or Plasma, LOINC via NLM Clinical Tables
  2. Basic Metabolic Panel (8), sample report (test 322758), Labcorp (2022)
4 more sources for the ranges and the explanation
  1. Pediatric Testing Reference Ranges (BUN/Creatinine Ratio, result 011577), Labcorp (2022)
  2. Comp. Metabolic Panel (14), sample report (test 322000), Labcorp (2022)
  3. Urea Nitrogen (BUN) (test 001040), Labcorp
  4. Acute Kidney Injury (AKI), Merck Manual Professional Edition, Merck Manual (2026)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. The calculator is version 1.0.0 of our code for this equation, tested against published examples. How we build and check these pages.

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