About

Blood glucose monitoring requires unit consistency. The United States reports plasma glucose in mg/dL (milligrams per deciliter), while most of Europe, Canada, and Australia use mmol/L (millimoles per liter). Misreading a value across systems introduces clinical risk. A fasting reading of 126 mg/dL flags diabetes; that same threshold is 7.0 mmol/L. Confusing the two can delay treatment or trigger false alarms. This converter applies the molar mass of glucose (M = 180.156 g/mol) to perform exact bidirectional conversion with clinical interpretation.

The tool classifies your result against WHO and ADA diagnostic thresholds for fasting, postprandial, and random glucose states. It approximates standard venous plasma readings. Capillary whole-blood values may differ by 10−15% depending on hematocrit. Always confirm with a laboratory assay before making clinical decisions.

Formulas

Glucose concentration conversion rests on the molar mass of D-glucose (C₆H₁₂O₆), which equals 180.156 g/mol. The deciliter-to-liter factor (10) combined with the milligram-to-gram factor (1000) simplifies to a single divisor of 18.0156.

C_mmol/L = C_mg/dL18.0156

C_mg/dL = C_mmol/L × 18.0156

Where C_mmol/L is the glucose concentration in millimoles per liter, and C_mg/dL is the concentration in milligrams per deciliter. The conversion factor 18.0156 derives from M10 where M = 180.156 g/mol is the molecular weight of glucose. Some references round to 18.02 or 18. This tool uses the precise 18.0156 value.

Reference Data

Condition / State	mg/dL	mmol/L	Context
Severe hypoglycemia	< 40	< 2.2	Medical emergency
Hypoglycemia	40 - 54	2.2 - 3.0	Symptomatic low
Low normal	55 - 69	3.1 - 3.8	Lower bound of normal
Normal fasting	70 - 99	3.9 - 5.5	ADA fasting target
Optimal fasting	80 - 90	4.4 - 5.0	Metabolically healthy
Prediabetes (fasting)	100 - 125	5.6 - 6.9	Impaired fasting glucose (IFG)
Diabetes (fasting)	≥ 126	≥ 7.0	ADA diagnostic threshold
Normal 2h post-meal	< 140	< 7.8	OGTT 2-hour value
Prediabetes (2h OGTT)	140 - 199	7.8 - 11.0	Impaired glucose tolerance (IGT)
Diabetes (2h OGTT)	≥ 200	≥ 11.1	ADA diagnostic threshold
Random diabetes diagnosis	≥ 200	≥ 11.1	With symptoms (polyuria, polydipsia)
Gestational target (fasting)	< 95	< 5.3	ACOG guideline
Gestational target (1h post)	< 140	< 7.8	ACOG guideline
Gestational target (2h post)	< 120	< 6.7	ACOG guideline
Pediatric normal (fasting)	70 - 100	3.9 - 5.6	Ages 6-12
Neonatal hypoglycemia	< 47	< 2.6	AAP threshold (first 48h)
ICU target range	140 - 180	7.8 - 10.0	ADA critical care
DKA threshold	≥ 250	≥ 13.9	Diabetic ketoacidosis risk
HHS threshold	≥ 600	≥ 33.3	Hyperosmolar hyperglycemic state
HbA1c 5.7% equivalent	117	6.5	eAG (estimated average glucose)
HbA1c 6.5% equivalent	140	7.8	eAG diabetes threshold
HbA1c 7.0% equivalent	154	8.6	ADA treatment target
HbA1c 8.0% equivalent	183	10.2	Poor control
HbA1c 9.0% equivalent	212	11.8	High risk of complications
HbA1c 10.0% equivalent	240	13.3	Urgent intervention needed

Frequently Asked Questions

The United States adopted mg/dL (mass concentration) early in clinical chemistry. Most other nations later adopted the SI system, which uses mmol/L (substance concentration). The SI unit is preferred by the International Federation of Clinical Chemistry because it reflects the actual number of glucose molecules, not just weight. Neither unit is inherently more accurate; they measure the same quantity expressed differently.

The mathematical conversion factor (18.0156) is constant because it derives from the molecular weight of glucose, a fixed physical property. However, the measured glucose value itself can vary by sample type. Venous plasma readings run approximately 10-15% higher than whole-blood capillary readings due to red blood cell glucose consumption. Temperature affects enzymatic assay kinetics in the lab, not the unit conversion. Always note whether your value comes from a lab plasma test or a home glucometer.

HbA1c reflects average glucose exposure over 8-12 weeks by measuring glycated hemoglobin as a percentage. The estimated Average Glucose (eAG) formula is: eAG (mg/dL) = 28.7 × HbA1c − 46.7. For example, an HbA1c of 7.0% corresponds to an eAG of approximately 154 mg/dL (8.6 mmol/L). This tool converts point-in-time readings, not time-averaged values. Use the reference table rows for HbA1c equivalents.

Per ADA (American Diabetes Association) 2024 Standards of Care: Normal fasting is below 100 mg/dL (5.6 mmol/L). Prediabetes (impaired fasting glucose) is 100-125 mg/dL (5.6-6.9 mmol/L). Diabetes is diagnosed at 126 mg/dL (7.0 mmol/L) or above on two separate occasions. These thresholds apply to venous plasma glucose after at least 8 hours of fasting.

The linear conversion is mathematically valid at any glucose concentration. However, at very high levels (above 600 mg/dL / 33.3 mmol/L), laboratory instruments may reach saturation limits, and the sample may need dilution, introducing measurement error unrelated to unit conversion. At the low end (below 20 mg/dL / 1.1 mmol/L), home glucometers lose accuracy due to electrochemical sensor limitations. The conversion itself remains exact.

Home glucometers measure capillary whole blood, while labs typically measure venous plasma. Plasma yields values roughly 11% higher than whole blood because plasma lacks red blood cells that consume glucose. Additionally, glucometer standards (ISO 15197:2013) allow ±15% error for readings above 100 mg/dL and ±15 mg/dL for readings at or below 100 mg/dL. Always calibrate expectations accordingly.