Free lab tool
BUN creatinine ratio calculator
Enter blood urea nitrogen (BUN) and serum creatinine from the same blood draw to calculate the BUN-to-creatinine ratio. Both values must be reported in mg/dL. The ratio is a nonspecific clue, not a diagnosis of dehydration, gastrointestinal bleeding, or kidney disease.
Formula and unit assumptions
This calculator uses the conventional-unit formula below. It does not convert urea to BUN or convert creatinine from µmol/L.
Example: 18 mg/dL BUN ÷ 1.0 mg/dL creatinine = 18, conventionally written as 18:1. BUN measures the nitrogen portion of urea, so a urea result in mmol/L cannot be substituted directly. Entering mixed units can produce a plausible-looking but clinically meaningless answer.
Educational interpretation table
The rows below are report-like educational categories, not diagnostic cutoffs. A commonly cited range is about 10:1–20:1, but reference ranges and reporting practices vary by laboratory.
| Calculated ratio | Report-style label | Educational context |
|---|---|---|
| Below 10:1 | Below the commonly cited range | May reflect relatively low BUN or relatively high creatinine. Nutrition, liver urea production, fluid status, muscle factors, and the individual results all matter. |
| 10:1–20:1 | Within the commonly cited range | Does not prove normal kidney function. BUN, creatinine, eGFR, urine testing, trends, and the laboratory’s own reference interval still need review. |
| Above 20:1 | Above the commonly cited range | Can occur with dehydration, reduced kidney blood flow, high protein intake, gastrointestinal bleeding, or other factors; it does not identify the cause. |
Use the reference interval printed on your own report. A ratio inside this broad range does not establish that BUN, creatinine, or kidney function is normal.
What this ratio cannot tell you
- It cannot diagnose dehydration. Fluid status requires clinical context, examination, and often other laboratory findings.
- It cannot diagnose gastrointestinal bleeding. Symptoms and appropriate medical evaluation matter more than the ratio.
- It cannot diagnose or stage kidney disease. Creatinine, eGFR, urine albumin, trends over time, and the broader clinical picture are used instead.
- It cannot explain which input is driving the result without reviewing BUN and creatinine separately.
Frequently asked questions
How do you calculate the BUN/creatinine ratio?
When both results are reported in mg/dL, divide blood urea nitrogen (BUN) by serum creatinine. For example, BUN 18 mg/dL divided by creatinine 1.0 mg/dL gives a ratio of 18:1. The calculation is not valid if you mix conventional and SI units.
What is a typical BUN/creatinine ratio?
A commonly cited adult range is approximately 10:1 to 20:1 when both BUN and creatinine are measured in mg/dL. Laboratories may use different reference intervals, so compare the result with the range on your own report and have it interpreted alongside the individual BUN, creatinine, eGFR, symptoms, and clinical history.
Does a high BUN/creatinine ratio mean dehydration?
No. Dehydration can raise the ratio, but so can a high-protein intake, gastrointestinal bleeding, corticosteroid use, and reduced blood flow to the kidneys. The ratio is nonspecific and cannot diagnose dehydration or identify its cause by itself.
Does the BUN/creatinine ratio diagnose kidney disease?
No. Kidney disease cannot be diagnosed from this ratio alone, and some kidney disorders may raise BUN and creatinine proportionally without producing a high ratio. Clinicians evaluate the individual creatinine, eGFR, urine albumin, changes over time, and other findings.
Can I enter urea in mmol/L or creatinine in µmol/L?
Not directly in this calculator. It expects BUN in mg/dL and creatinine in mg/dL; urea is not the same measurement as BUN, and creatinine in µmol/L is a different unit. Convert both values correctly or use results already reported in conventional units before calculating.
When should I seek urgent medical help?
The ratio itself has no single emergency cutoff. Seek urgent care for symptoms such as vomiting blood, black or tarry stools, fainting, severe weakness, very low urine output, confusion, chest pain, or shortness of breath, regardless of the calculated ratio.
Learn about the individual results
Sources
This page draws on the following authoritative references.
- BUN (Blood Urea Nitrogen) — MedlinePlus, National Library of Medicine
- Creatinine Test — MedlinePlus, National Library of Medicine
- Glomerular Filtration Rate (GFR) Test — MedlinePlus, National Library of Medicine
- BUN and Creatinine — Clinical Methods, National Center for Biotechnology Information
- Acute Kidney Injury (AKI) — Merck Manual Professional Edition
Medically reviewed by Antonieta Rueda, MD and Kyle R. Toth, MD · Last reviewed August 1, 2026
This calculator and its educational categories provide general information only. They are not medical advice, do not diagnose any condition, and are not a substitute for interpretation by a qualified healthcare professional who can review your complete lab report, symptoms, medical history, and medications. Do not delay urgent care because of a calculator result.