BUN Creatinine Ratio Calculator

Quick Answer

Last updated: 11 November 2026 ·How we calculate this: BUN ÷ creatinine (StatPearls, Clinical Methods)

How This BUN Creatinine Ratio Calculator Works

Blood urea nitrogen (BUN) and creatinine are both waste products that the kidneys clear, and they appear together on a basic or comprehensive metabolic panel. Comparing them helps tell apart problems before the kidneys (such as dehydration), in the kidneys and after them. Choose the units on your lab report, enter BUN (or urea) and creatinine, and press Calculate. The calculator converts SI units, gives the ratio and its category, and notes what a high or low ratio is often linked with.

How to Use the BUN Creatinine Ratio Calculator

1. Choose US units (mg/dL) or SI units (urea mmol/L, creatinine µmol/L).
2. Enter the BUN or urea result.
3. Enter the creatinine result.
4. Press Calculate.
5. Read the ratio, its category and what it is often linked with.

BUN Creatinine Ratio Formulas

• Ratio: BUN (mg/dL) ÷ creatinine (mg/dL)
• Urea to BUN: BUN (mg/dL) = urea (mmol/L) × 2.801
• Creatinine units: mg/dL = µmol/L ÷ 88.4
• SI ratio: urea (mmol/L) ÷ creatinine (mmol/L), about 4 times the US ratio, so roughly 40 to 80 for the same 10-20 range
• Usual BUN: 5 to 20 mg/dL (1.8 to 7.1 mmol/L urea)

Key Terms

• BUN: blood urea nitrogen, the nitrogen part of urea in the blood.
• Urea: the main waste product of protein, reported in mmol/L in SI units.
• Creatinine: a waste product of muscle, filtered by the kidneys.
• Pre-renal: a cause before the kidneys, such as dehydration or low blood flow.
• Intrinsic renal: a problem in the kidney tissue itself.

Worked Example

A UK lab reports urea 5.0 mmol/L and creatinine 80 µmol/L. What is the BUN:creatinine ratio?

• BUN = 5.0 × 2.801 = 14.0 mg/dL
• Creatinine = 80 ÷ 88.4 = 0.90 mg/dL
• Ratio = 14.01 ÷ 0.905 = 15.5 : 1, in the usual range

Another person has BUN 40 mg/dL and creatinine 1.0 mg/dL: the ratio is 40:1, very high, which often goes with dehydration or bleeding in the upper gut.

Real-Life Examples

• Lab reports: some panels list the ratio; others do not, so work it out.
• SI reports: convert UK, Irish or European urea and creatinine to the US ratio.
• Hydration: a rising ratio can be a sign of dehydration.
• Study: see how BUN and creatinine move together.

BUN vs Creatinine

• BUN: nitrogen from urea, made by the liver from protein; changes with diet and hydration.
• Creatinine: made by muscles at a steady rate; a better guide to kidney filtration.
• Together: the ratio shows whether BUN is out of step with creatinine.

BUN Creatinine Ratio Examples

Ratios of about 10 to 20 are usual.

What Changes the Ratio

BUN rises when the body breaks down more protein or reabsorbs more urea: dehydration, heart failure with poor kidney blood flow, a high-protein diet, corticosteroids, and blood in the upper digestive tract (which is digested like protein) all push the ratio up. BUN falls with low protein intake, severe liver disease (the liver makes urea) and pregnancy, which pull the ratio down.

Creatinine depends on muscle mass. Older adults and people with little muscle have low creatinine, so their ratio can look high even when BUN is only a little raised. Very muscular people and those who eat a lot of meat or take creatine have higher creatinine and a lower ratio. That is why doctors read the ratio alongside each value, the eGFR, the urine and the person’s history, never alone.

Common Mistakes to Avoid

• Mixing units. Use mg/dL for both, or convert urea and µmol/L first.
• Treating urea as BUN. Urea in mg/dL is 2.14 times BUN; in mmol/L multiply by 2.801.
• Reading the ratio alone. Check each value and the eGFR too.
• Ignoring muscle mass. Low creatinine can raise the ratio without disease.
• Self-diagnosing. Ask the doctor who ordered the test.

Frequently Asked Questions

References & Sources