What is mmol/L and how does it differ from mg/dL?

mmol/L (millimoles per liter) and mg/dL (milligrams per deciliter) are both units used to measure the concentration of substances in blood. The US primarily uses mg/dL (a mass-based measurement), while most other countries use mmol/L (a molar-based measurement from the SI system). The conversion factor differs for each substance because it depends on the molecular weight. For blood glucose, 1 mmol/L equals approximately 18 mg/dL.

How do I convert blood sugar from mg/dL to mmol/L?

To convert blood sugar (glucose) from mg/dL to mmol/L, divide by 18.018 (or multiply by 0.0555). For example, a fasting glucose of 100 mg/dL equals approximately 5.6 mmol/L. To convert the other way, multiply mmol/L by 18.018. A normal fasting blood sugar is 70-100 mg/dL or 3.9-5.6 mmol/L.

Why do different countries use different units for blood tests?

The difference stems from the adoption of the International System of Units (SI). In 1960, the General Conference on Weights and Measures established SI units as the global standard for scientific measurement. Most countries adopted SI units for medical labs, using mmol/L for concentrations. The United States, however, retained its conventional units (mg/dL, mEq/L) due to the cost and complexity of converting its large healthcare infrastructure. This means the same blood test result is reported in different numbers depending on the country.

Lab & Blood Test Unit Converter

By KAMP Inc. / UnitOwl · Last reviewed: April 3, 2026

Convert lab test values between US conventional units and SI (international) units. Select a test, enter your value, and see the conversion with reference ranges.

Medical Disclaimer: Reference ranges shown are general guidelines only and may differ from your laboratory's specific ranges. Lab results must be interpreted by a qualified healthcare provider in the context of your personal medical history. Do not use this tool to self-diagnose or make treatment decisions.

Select Lab Test

Value in mg/dL

mg/dL

Normal range: 70-100 mg/dL

Result in mmol/L

5.55 mmol/L

Normal range: 3.9-5.6 mmol/L

Within normal range

All Lab Test Reference Ranges

Test	US Unit	Normal (US)	SI Unit	Normal (SI)
Glucose (fasting)	mg/dL	70-100	mmol/L	3.9-5.6
Cholesterol (total)	mg/dL	<200	mmol/L	<5.2
HDL Cholesterol	mg/dL	>40	mmol/L	>1.0
LDL Cholesterol	mg/dL	<100	mmol/L	<2.6
Triglycerides	mg/dL	<150	mmol/L	<1.7
Creatinine	mg/dL	0.7-1.3	µmol/L	62-115
Hemoglobin	g/dL	12-17.5	g/L	120-175
HbA1c	%	<5.7	mmol/mol	<39
Calcium	mg/dL	8.5-10.5	mmol/L	2.1-2.6
Potassium	mEq/L	3.5-5.0	mmol/L	3.5-5.0
Sodium	mEq/L	136-145	mmol/L	136-145
Uric Acid	mg/dL	3.5-7.2	µmol/L	208-428
Bilirubin	mg/dL	0.1-1.2	µmol/L	2-21
Vitamin D	ng/mL	30-100	nmol/L	75-250
Iron	µg/dL	60-170	µmol/L	11-30
TSH	mIU/L	0.4-4.0	mIU/L	0.4-4.0

Disclaimer: This tool is for informational purposes only. Lab reference ranges may vary between laboratories. Always consult your healthcare provider for interpretation of your lab results.

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Why Are Lab Units Different in the US vs. Other Countries?

If you've ever received blood test results from a different country, you may have noticed the numbers look completely different — even though the test is the same. This is because the United States uses "conventional" units (like mg/dL for glucose), while most other countries use SI (Système International) units (like mmol/L).

The SI system, adopted internationally in 1960, measures concentrations in moles per liter — a unit based on the number of molecules rather than their weight. The US system measures in mass per volume (milligrams per deciliter). Because each substance has a different molecular weight, the conversion factor is unique to each test. You can't use one conversion factor for all lab values.

This distinction matters most for patients who travel internationally, consult doctors in different countries, or read medical research published in international journals. The converter above handles the math for 16 of the most common blood tests, so you can quickly understand your results in either system.

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Understanding Common Blood Tests

Glucose (fasting): Measures blood sugar after 8+ hours without eating. Normal is 70-100 mg/dL (3.9-5.6 mmol/L). Levels of 100-125 mg/dL indicate prediabetes, while 126+ mg/dL suggests diabetes.

HbA1c (glycated hemoglobin): Reflects average blood sugar over the past 2-3 months. Unlike most tests, HbA1c uses a special conversion formula between percentage (US) and mmol/mol (IFCC/SI). The formula is: mmol/mol = (HbA1c% - 2.15) × 10.929. Normal is below 5.7% (39 mmol/mol).

Cholesterol panel: Total cholesterol, HDL ("good"), LDL ("bad"), and triglycerides are all measured in mg/dL in the US and mmol/L elsewhere. All three cholesterol types use the same conversion factor (0.0259), but triglycerides use a different factor (0.0113) because triglyceride molecules have a different molecular weight.

Hemoglobin: Measures the oxygen-carrying protein in red blood cells. The US uses g/dL while SI uses g/L — a simple factor of 10. Normal ranges are 12-17.5 g/dL (120-175 g/L), varying by sex and age.

Important Notes About Reference Ranges

The reference ranges shown in this converter are general guidelines based on commonly used laboratory standards. Your lab may use slightly different ranges depending on the testing equipment and methodology. Always compare your results to the specific reference ranges printed on your lab report.

Reference ranges can also vary based on age, sex, and pregnancy status. For example, hemoglobin ranges are typically higher for men (13.5-17.5 g/dL) than women (12-16 g/dL). Creatinine levels differ between adults and children. Pregnant women have different normal ranges for many tests.

A result outside the normal range does not necessarily indicate a medical problem — it means further evaluation may be warranted. Only your healthcare provider can interpret your results in the context of your overall health, medications, and medical history.

Sources & References

Bureau International des Poids et Mesures (BIPM) — SI Units — The international authority defining the SI (Système International) measurement system.
NIST Special Publication 811 — Guide for the Use of SI Units — U.S. National Institute of Standards and Technology guide to SI unit usage and conversions.
World Health Organization (WHO) — Use of Glycated Haemoglobin (HbA1c) in Diagnosis of Diabetes Mellitus — WHO guidance on HbA1c reference values and diabetes diagnosis criteria.
International Federation of Clinical Chemistry (IFCC) — International standards for clinical laboratory measurements and reference intervals.

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