# BUN to Creatinine Ratio Calculator

URL: https://speedycalculator.com/calculators/health/bun-creatinine-ratio/
Last updated: 2026-10-30

> The BUN to creatinine ratio calculator divides blood urea nitrogen by creatinine to help tell whether acute kidney injury is pre-renal (from dehydration or low blood flow), intrinsic or post-renal, with conversions from urea and µmol/L units.

## Inputs

- BUN (mg/dL, mmol/L urea)
- Creatinine (mg/dL, µmol/L)

## Results

- BUN/creatinine ratio
- Urea/creatinine ratio (UK units, mmol/µmol)

## Formula

```
BUN/Cr ratio = BUN (mg/dL) ÷ creatinine (mg/dL)
> 20: pre-renal or upper GI bleeding · 10–20: normal or post-renal · < 10: intrinsic kidney damage, liver disease or low protein intake
```

## Explanation

Urea is reabsorbed in the kidney when blood flow is low, while creatinine is not, so dehydration raises the ratio. The ratio is a clue rather than a diagnosis – high-protein diets, steroids and gut bleeding also raise it.

### How to use the BUN to Creatinine Ratio Calculator

- **BUN**
- **Creatinine**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Enter BUN (or urea) and creatinine from the same blood test.

### Inputs explained

FieldWhat to enterBUNUnits: mg/dL, mmol/L ureaCreatinineUnits: mg/dL, µmol/L

### What each result means

- **BUN/creatinine ratio** = [BUN]÷[Creatinine]
- **Urea/creatinine ratio (UK units, mmol/µmol)** = ([BUN]÷2.8)÷([Creatinine]×88.42)×1000

### Example values

How the main result changes when **BUN** changes and everything else stays at the example values above:

BUN (mg/dL)BUN/creatinine ratio101015152020252530304040
*Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.*

## Worked example

Inputs — BUN: 20 mg/dL; Creatinine: 1 mg/dL.

Results — **BUN/creatinine ratio = 20**; Urea/creatinine ratio (UK units, mmol/µmol) = 81.

## Key terms

- **BUN**: Blood urea nitrogen.

## FAQ

**What is a normal BUN/creatinine ratio?**
About 10–20.

**What does a high ratio mean?**
Often dehydration, heart failure, gut bleeding or a high-protein diet.

**What does a low ratio mean?**
Liver disease, malnutrition or intrinsic kidney damage.


## Sources

- [Hosten AO. BUN and creatinine. Clinical Methods, 3rd ed.](https://www.ncbi.nlm.nih.gov/books/NBK305/)