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About this tool
Convert between blood urea nitrogen and urea in mg/dL and mmol/L, with the BUN to creatinine ratio and reference intervals.
The Urea and BUN Converter translates a kidney-function result between blood urea nitrogen in mg/dL, urea in mg/dL and urea in mmol/L. BUN counts only the nitrogen inside the urea molecule, so urea is 2.14 times the BUN figure — the ratio of urea's molar mass, 60.06 g/mol, to the 28.014 g/mol of its two nitrogen atoms. It also derives the BUN to creatinine ratio, which is read against the familiar 10:1 and 20:1 teaching bands.
Open Urea and BUN Converter on AltFTool — it loads instantly in your browser.
Enter the values you already know.
Fine-tune the options to match your scenario.
Read the result and use it in your planning or reporting.
BUN mg/dL, urea mg/dL and urea mmol/L are shown together, so nothing has to be chained by hand.
Uses 2.1439 for the urea-to-nitrogen step and 6.006 mg/dL per mmol/L, rather than a rounded shortcut.
Adds the BUN to creatinine ratio in mg/dL, the basis on which the 10:1 and 20:1 bands are defined.
They measure the same substance on two different bases. BUN reports only the nitrogen content of urea, while a urea result reports the whole molecule, so urea equals BUN × 2.14. A BUN of 14 mg/dL is the same sample as a urea of 30 mg/dL, or 5.0 mmol/L.
Multiply the BUN by 0.357. So a BUN of 14 mg/dL is 5.0 mmol/L urea and a BUN of 20 mg/dL is 7.1 mmol/L. That single factor combines the 2.1439 urea-to-nitrogen mass ratio with the 6.006 mg/dL that make up 1 mmol/L of urea.
Most laboratories quote roughly 7 to 20 mg/dL for adults, which is about 2.5 to 7.1 mmol/L of urea. Intervals differ between laboratories and rise with age, so compare against the range printed on your own report.
A ratio above 20:1 is classically linked to prerenal causes — dehydration, heart failure, or a gastrointestinal bleed that delivers a protein load to the gut — while a ratio below 10:1 points more towards intrinsic kidney disease, a low-protein diet or liver disease. These are orientation bands rather than diagnostic rules, and they are read alongside eGFR, urine tests and the clinical picture.
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