What is the difference between BUN and serum urea?

Both measure the same metabolite (urea) in blood, but BUN reports only the nitrogen portion of urea, so BUN = urea × (28/60) ≈ urea × 0.4667. Serum urea measures the entire urea molecule. The US primarily reports BUN; most other countries report serum urea in mmol/L.

What conversion factor is used?

The standard clinical factor: 1 mmol/L urea = 2.8 mg/dL BUN. Each millimole of urea contains 28 mg of nitrogen (2 × 14 mg/mmol); dividing 28 mg/L by 10 dL/L yields 2.8 mg/dL BUN.

Does this converter say whether my result is normal?

No. Reference intervals vary by laboratory method, age, clinical setting and population. Compare the converted value with the interval printed by the laboratory and discuss interpretation with a clinician.

Is this tool suitable for clinical decision-making?

It performs a unit conversion using standard rounded factors. It does not validate a laboratory measurement, diagnose kidney function or replace clinical interpretation.

Can I convert urea mg/dL to mmol/L?

Yes. Enter the urea mg/dL value in the Urea (mg/dL) field and the tool will calculate both urea mmol/L and BUN mg/dL automatically. The factor is: mmol/L = mg/dL ÷ 6.006.

BUN to Urea Converter

Convert in either direction among BUN mg/dL, serum urea mmol/L and serum urea mg/dL. The tool reports units explicitly and does not diagnose a lab result.

Enter Any Value

Type in any one field and the other two update instantly.

BUN (mg/dL)

Blood urea nitrogen — US convention

Serum Urea (mmol/L)

SI units — used in most countries

Serum Urea (mg/dL)

Urea as full molecule in mg/dL

Converted values

Enter a value on the left to see the result.

Conversion Formulas

Urea (mmol/L) = BUN (mg/dL) ÷ 2.8

Urea (mg/dL) = BUN (mg/dL) ÷ 0.4667

BUN (mg/dL) = Urea (mmol/L) × 2.8

Urea (mg/dL) = Urea (mmol/L) × 6.006

The 2.8 factor follows from 28 mg of nitrogen per mmol of urea and conversion from mg/L to mg/dL. Factors are rounded for clinical unit conversion.

Source: NCBI/PMC conventional-to-SI conversion table.

Interpretation boundary

Use the reference interval supplied with the original laboratory report. Do not apply a generic web threshold to make a diagnosis or change treatment.

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Summary

Blood urea nitrogen (BUN) and serum urea express related quantities differently. BUN reports the mass of nitrogen contained in urea, while serum urea reports the whole urea molecule. This calculator converts among BUN mg/dL, urea mmol/L and urea mg/dL using standard clinical conversion factors; it does not interpret whether a result is normal or abnormal.

How it works

Enter a numeric value in the BUN (mg/dL), Urea (mmol/L), or Urea (mg/dL) field.
The tool detects which field you typed in and converts to the other two in real time.
Conversion uses the standard factor: 1 mmol/L urea = 2.8 mg/dL BUN (molecular weight ratio of nitrogen to urea).
Results are rounded to two decimal places for readable unit conversion.
Use the Copy button next to any result to copy its value to the clipboard.

Use cases

Interpret lab reports from different countries that use BUN vs. urea conventions.
Convert US-standard BUN (mg/dL) to SI urea (mmol/L) for academic or publication use.
Cross-reference kidney function panels reported in different units.
Verify manual conversions when reading nephrology literature.
Assist medical students learning the relationship between BUN and urea.
Support telemedicine consultations involving patients with international lab results.

Frequently Asked Questions

Last updated: 2026-09-15 · Reviewed by Nham Vu