BUN to Creatinine Ratio Calculator

Calculate the BUN to creatinine ratio, a lab clue that helps separate dehydration and bleeding from kidney-related causes of a high creatinine. Example: BUN 28 and creatinine 1.0 gives a ratio of 28, above the usual 10 to 20 range.

Try it

Ratio & Proportion Calculator

Open the full calculator →

Type the problems from this lesson and check each step.

FreeNo sign-up

BUN (mg/dL)

Creatinine (mg/dL)

How to use the BUN to Creatinine Ratio Calculator

Enter the values in the fields.
Press Calculate to see the result with the steps shown.

Formula and method

BUN:creatinine ratio = BUN (mg/dL) / serum creatinine (mg/dL). Normal is about 10 to 20.

Interpreting the ratio

Ratio	Typical pattern
Below 10	Low protein intake, liver disease, overhydration
10 to 20	Normal
Above 20	Prerenal (dehydration, heart failure), GI bleed, high protein

If your BUN is in mmol/L

Urea in SI units: multiply urea (mmol/L) by 2.8 to get BUN in mg/dL, and creatinine (umol/L) divided by 88.4 gives mg/dL.

Ratio patterns

BUN	Creatinine	Ratio
12	1.0	12
18	0.9	20
40	1.2	33
60	4.0	15

Limits

This calculator is for education and is not medical advice. Lab and clinical decisions belong with a qualified clinician who sees the whole picture.

Frequently asked questions

What is a normal BUN to creatinine ratio?

10 to 20.

What causes a high ratio?

Dehydration, low kidney blood flow, GI bleeding, high protein diet.

What causes a low ratio?

Low protein intake, liver disease, overhydration.

Is a high ratio dangerous?

It depends on the cause; talk to a clinician.

Does ratio replace GFR?

No.

How do I convert units?

See the unit conversion section.

Sources

Related calculators

Browse all calculators

Effortless Math Team

11 minutes ago