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. Derived from the molecular weight of urea (60 g/mol) and two nitrogen atoms (2 × 14 = 28 g/mol), giving a ratio of 28/60 × 6 = 2.8.

What are normal BUN and urea reference ranges?

Normal BUN is roughly 7–20 mg/dL (2.5–7.1 mmol/L urea). Values above 20 mg/dL BUN (7.1 mmol/L urea) may indicate reduced kidney function, dehydration, or high protein intake. Always interpret results in clinical context.

Is this tool accurate for clinical decision-making?

The conversion formulas are mathematically exact. However, this tool is for educational and reference purposes only. Always rely on a certified laboratory and a qualified clinician for medical decisions.

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

Name: BUN to Urea Converter
Availability: InStock
Author: Nham Vu

Convert BUN (mg/dL) to serum urea (mmol/L or mg/dL) and back — instantly, with the exact formulas used in clinical labs.

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

Result & Status

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

Factor 2.8 = 2 × 14 (nitrogen MW) ÷ 60 (urea MW) × 6

Adult Reference Ranges

Unit	Low	Normal	High
BUN mg/dL	< 7	7 – 20	> 20
Urea mmol/L	< 2.5	2.5 – 7.1	> 7.1
Urea mg/dL	< 15	15 – 43	> 43

Reference ranges are approximate for adults. Always consult a clinician.

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Summary

Convert BUN (mg/dL) to serum urea (mmol/L or mg/dL) and back — instantly, with the exact formulas used in clinical labs.

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 clinical precision.
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: 2026-06-09 · Reviewed by Nham Vu