BUN Creatinine Ratio Calculator

Q: What is a normal BUN Creatinine ratio?

A normal BUN/Creatinine ratio is between 10 and 20 . This means your kidneys, liver, and hydration levels are likely in good shape. A result outside this range does not always mean you are sick, but it is worth discussing with your doctor.

Q: Do I need to fast before taking a BUN or creatinine blood test?

Most labs do not require fasting for a BUN or creatinine test. However, eating a large amount of meat or protein shortly before the test can temporarily raise your BUN level. Follow any instructions your doctor or lab gives you.

Q: How is BUN different from creatinine?

BUN comes from the breakdown of protein you eat. It is made in the liver and removed by the kidneys. Creatinine comes from normal muscle activity and is produced at a fairly steady rate each day. Both are filtered by the kidneys, but BUN is more easily affected by diet, hydration, and other body processes.

Bun Creatinine Ratio Calculator

Updated Sep 3, 2026 By Jehan Wadia

BUN/Creatinine Ratio Interpretation Reference
BUN/Cr Ratio	Classification	Clinical Implication
< 10	Low	Possible liver disease, malnutrition, or over-hydration
10 – 20	Normal	Within expected reference range
21 – 25	Elevated	Possible early dehydration or protein imbalance
> 25	High	Possible pre-renal azotemia, dehydration, or GI bleed

BUN/Creatinine Ratio Interpretation Reference

BUN/Cr Ratio

Classification

Clinical Implication

< 10

Low

Possible liver disease, malnutrition, or over-hydration

10 – 20

Normal

Within expected reference range

21 – 25

Elevated

Possible early dehydration or protein imbalance

> 25

High

Possible pre-renal azotemia, dehydration, or GI bleed

Introduction

The BUN Creatinine Ratio Calculator divides your blood urea nitrogen (BUN) level by your serum creatinine level. Both of these are waste products that your kidneys filter out of your blood. When they are in balance, your kidneys are likely working well. When the ratio is too high or too low, it can be a sign that something needs attention.

Doctors use the BUN/Creatinine ratio to help tell the difference between kidney problems and other health issues like dehydration, heart failure, liver disease, or bleeding in the gut. A ratio of about 10 to 20 is the range usually treated as typical. A ratio above 20 is the traditional threshold for a prerenal cause such as dehydration, although studies show it should never be read on its own.¹ Values outside the typical range give your doctor clues about what may be going on inside your body.

This calculator lets you enter your BUN and creatinine lab results in either common or international units. It then shows your ratio, places it on a color-coded scale, and explains what the result means. You also get a full step-by-step breakdown of the math so you can see exactly how the number is found. Use it as a quick reference tool, but always discuss your results with your healthcare provider for a proper diagnosis.

How to Use Our BUN Creatinine Ratio Calculator

Enter your lab test results below to calculate your BUN/Creatinine ratio. The calculator will show your ratio, tell you if it is low, normal, elevated, or high, and explain what it means.

Blood Urea Nitrogen (BUN): Type your BUN value from your blood test. Choose mg/dL or mmol/L to match the units on your lab report. A typical reference range for BUN is 6 to 20 mg/dL.²

Serum Creatinine: Type your creatinine value from your blood test. Choose mg/dL or µmol/L to match the units on your lab report. Typical reference ranges are 0.7 to 1.3 mg/dL for men and 0.5 to 0.95 mg/dL for women.³

Click Calculate to see your result. Click Reset to clear all fields and start over.

What Is the BUN/Creatinine Ratio?

The BUN/Creatinine ratio compares two waste products in your blood: blood urea nitrogen (BUN) and creatinine. Both are filtered out by your kidneys. BUN comes from the breakdown of protein in the food you eat. Creatinine comes from normal muscle activity. A simple blood test measures both numbers, and dividing BUN by creatinine gives you the ratio.

Why Does This Ratio Matter?

Your kidneys clean your blood every day. When they work well, BUN and creatinine stay in a balanced range. If the ratio is too high or too low, it can be a sign that something is off. Doctors use this ratio as one clue to check how your kidneys, liver, and overall hydration are doing. It is not a diagnosis on its own, but it helps point doctors in the right direction.

How to Calculate the BUN/Creatinine Ratio

The formula is straightforward:

BUN/Creatinine Ratio = BUN (mg/dL) ÷ Creatinine (mg/dL)

Both values must be in the same unit (mg/dL) before you divide. If your lab results use mmol/L for BUN or µmol/L for creatinine, the calculator above converts them for you automatically.

What Do the Results Mean?

Below 10 (Low): This may point to liver problems, not eating enough protein, or having too much fluid in the body.
10 to 20 (Normal): This is the healthy range for most adults. It means your kidneys and liver are likely working as expected.
21 to 25 (Elevated): This can be an early sign of dehydration or a shift in protein balance. It deserves attention but is not always serious.
Above 25 (High): This may signal dehydration, heart failure, bleeding in the stomach or intestines, or a condition called pre-renal azotemia, where blood flow to the kidneys drops.

What Can Affect Your Results?

Several things can change your BUN level without meaning your kidneys are sick. Eating a lot of protein raises BUN. Not drinking enough water raises it too. Certain medicines, intense exercise, and aging can also shift the numbers. That is why doctors always look at the full picture, not just one ratio, before making decisions about your health.

When Should You Talk to a Doctor?

If your BUN/Creatinine ratio falls outside the normal range, share your results with your doctor. A single abnormal result does not always mean something is wrong. Your doctor may order follow-up tests like a glomerular filtration rate (GFR), urine tests, or imaging to get a clearer view of your kidney health. Early detection of kidney problems gives you the best chance for effective treatment.

Formulas used

BUN/Creatinine Ratio ¹

\text{BUN/Cr Ratio} = \dfrac{\text{BUN (mg/dL)}}{\text{Creatinine (mg/dL)}}

BUN Conversion (mmol/L to mg/dL)

\text{BUN (mg/dL)} = \dfrac{\text{BUN (mmol/L)}}{0.357}

Creatinine Conversion (µmol/L to mg/dL)

\text{Creatinine (mg/dL)} = \dfrac{\text{Creatinine (}\mu\text{mol/L)}}{88.4}

Frequently asked questions

What is a normal BUN Creatinine ratio?

A normal BUN/Creatinine ratio is between 10 and 20. This means your kidneys, liver, and hydration levels are likely in good shape. A result outside this range does not always mean you are sick, but it is worth discussing with your doctor.

What does a BUN Creatinine ratio above 20 mean?

A ratio above 20 is the traditional threshold for a prerenal cause, such as dehydration or reduced blood flow to the kidneys, though studies have found it is not reliable on its own.¹ A very high-protein diet can also raise it. Bleeding in the stomach or intestines and heart failure can also raise the ratio. Your doctor will use other tests to find the exact cause.

What does a BUN Creatinine ratio below 10 mean?

A ratio below 10 may point to liver disease, a low-protein diet, malnutrition, or too much fluid in the body. Muscle wasting can also lower the ratio because it raises creatinine relative to BUN. Talk to your doctor if your result is in this range.

Do I need to fast before taking a BUN or creatinine blood test?

Most labs do not require fasting for a BUN or creatinine test. However, eating a large amount of meat or protein shortly before the test can temporarily raise your BUN level. Follow any instructions your doctor or lab gives you.

Can medications change my BUN Creatinine ratio?

Yes. Some drugs can raise BUN, including corticosteroids, certain antibiotics, and diuretics (water pills). Other drugs may affect creatinine levels. Always tell your doctor about all medicines and supplements you take so they can interpret your results correctly.

How is BUN different from creatinine?

BUN comes from the breakdown of protein you eat. It is made in the liver and removed by the kidneys. Creatinine comes from normal muscle activity and is produced at a fairly steady rate each day. Both are filtered by the kidneys, but BUN is more easily affected by diet, hydration, and other body processes.

How often should I check my BUN Creatinine ratio?

Most healthy adults get this checked during routine blood work once a year. If you have kidney disease, diabetes, high blood pressure, or heart disease, your doctor may want to check it more often, sometimes every few months.

Can dehydration alone cause a high ratio?

Yes. Dehydration is one of the most common reasons for a high BUN/Creatinine ratio. When your body does not have enough water, the kidneys hold on to more urea, which raises BUN while creatinine stays about the same. Drinking enough fluids usually brings the ratio back to normal.

Is the BUN Creatinine ratio enough to diagnose kidney disease?

No. This ratio is a helpful screening tool, but it cannot diagnose kidney disease on its own. Doctors also look at your GFR, urine tests, imaging, blood pressure, and medical history before making a diagnosis. Always share your results with a healthcare provider.

Does age affect the BUN Creatinine ratio?

It can. Older adults often have slightly higher BUN levels because kidney function naturally declines with age. Muscle mass also decreases, which can lower creatinine. This combination can push the ratio higher even when no disease is present. Your doctor will account for your age when reading results.

What should I do if my result says elevated or high?

Do not panic. A single high reading does not mean you have a serious problem. Drink plenty of water, note what you ate before the test, and share the result with your doctor. They may ask you to retest or run additional labs to find out what is causing the change.

Sources

Uchino S, Bellomo R, Goldsmith D. The meaning of the blood urea nitrogen/creatinine ratio in acute kidney injury. Clinical Kidney Journal. 2012;5(2):187-191. doi:10.1093/ckj/sfs013. Accessed September 3, 2026.

BUN (blood urea nitrogen) test. MedlinePlus, U.S. National Library of Medicine. Accessed September 3, 2026.

Creatinine blood test. MedlinePlus, U.S. National Library of Medicine. Accessed September 3, 2026.

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