Understanding Lab Units: mg/dL, mmol/L, and Common Conversions

Overview.

Lab results can be reported in different units depending on your country, lab, or test type. The same measurement might be 'mg/dL' in the US and 'mmol/L' in Europe—leading to confusion when comparing results or reading research. This guide explains common units, how to convert between them, and why understanding units matters for interpreting your health data.

Context: A glucose of 100 is concerning in mg/dL (prediabetes range) but excellent in mmol/L (would equal 5.6—optimal). Without understanding units, you might panic over a normal result or miss an abnormal one. Different labs may use different units, making comparison confusing without proper conversion.

Key takeaways.

• US labs typically use mg/dL; most other countries use mmol/L
• Glucose: mg/dL ÷ 18 = mmol/L (or mmol/L × 18 = mg/dL)
• Cholesterol: mg/dL ÷ 38.67 = mmol/L
• Triglycerides: mg/dL ÷ 88.57 = mmol/L
• Always check units before comparing to reference ranges
• When in doubt, ask your provider or use Gevety to auto-convert

Common Unit Systems.

Laboratory measurements use different unit systems depending on what's being measured and where you are in the world:

mg/dL

Milligrams per deciliter. Common in US for glucose, cholesterol, and many other tests. Measures mass per volume.

mmol/L

Millimoles per liter. International standard for glucose and lipids. Measures molecular concentration.

µg/dL or mcg/dL

Micrograms per deciliter. Used for iron, vitamin levels, and some hormones.

ng/mL or ng/dL

Nanograms per milliliter/deciliter. Common for vitamins (D, B12) and some hormones.

pg/mL

Picograms per milliliter. Very small concentrations, used for some hormones like Free T3.

mIU/L or µIU/mL

Milli-international units per liter. Used for TSH, insulin, and other hormones measured by activity.

IU/mL or U/L

International units per milliliter/liter. Common for enzymes like ALT, AST, and antibody titers.

g/dL

Grams per deciliter. Used for hemoglobin and albumin.

%

Percentage. Used for HbA1c, hematocrit, and iron saturation.

Key Conversion Formulas.

These are the most common conversions you'll need when comparing results:

Glucose

mg/dL ÷ 18 = mmol/L | Example: 100 mg/dL = 5.6 mmol/L

Cholesterol (Total, LDL, HDL)

mg/dL ÷ 38.67 = mmol/L | Example: 200 mg/dL = 5.2 mmol/L

Triglycerides

mg/dL ÷ 88.57 = mmol/L | Example: 150 mg/dL = 1.7 mmol/L

Creatinine

mg/dL × 88.4 = µmol/L | Example: 1.0 mg/dL = 88.4 µmol/L

Uric Acid

mg/dL × 59.48 = µmol/L | Example: 5.0 mg/dL = 297 µmol/L

Calcium

mg/dL ÷ 4 = mmol/L | Example: 10 mg/dL = 2.5 mmol/L

Hemoglobin

g/dL × 10 = g/L | Example: 14 g/dL = 140 g/L

Reference Ranges by Region.

Here are common reference ranges in both unit systems for key markers:

Fasting Glucose

Normal: <100 mg/dL or <5.6 mmol/L | Prediabetes: 100-125 mg/dL or 5.6-6.9 mmol/L | Diabetes: ≥126 mg/dL or ≥7.0 mmol/L

Total Cholesterol

Desirable: <200 mg/dL or <5.2 mmol/L | Borderline: 200-239 mg/dL | High: ≥240 mg/dL

LDL Cholesterol

Optimal: <100 mg/dL or <2.6 mmol/L | Near optimal: 100-129 mg/dL | Borderline high: 130-159 mg/dL

Triglycerides

Normal: <150 mg/dL or <1.7 mmol/L | Borderline: 150-199 mg/dL | High: 200-499 mg/dL

HbA1c

Normal: <5.7% | Prediabetes: 5.7-6.4% | Diabetes: ≥6.5% (same worldwide)

Common mistakes.

• Assuming all glucose values are in the same units (100 mg/dL ≠ 100 mmol/L)
• Comparing results from different labs without checking units
• Using online reference ranges without confirming they match your units
• Forgetting that some tests (like HbA1c) use the same units worldwide
• Not realizing mmol/L is smaller numerically than mg/dL for most tests
• Confusing mIU/mL with µIU/mL (they're the same—different notation)

Pro tips.

FAQs.