Glucose and HbA1c unit conversion calculator

Metabolic Tools

Glucose and HbA1c Calculator

Q: What is a normal fasting blood sugar level?

A normal fasting blood glucose level is below 5.6 mmol/L (100 mg/dL). Levels between 5.6 and 6.9 mmol/L (100–125 mg/dL) are classified as impaired fasting glucose (prediabetes), and a fasting glucose of 7.0 mmol/L (126 mg/dL) or above suggests diabetes. This should be confirmed with a repeat test.

Q: What HbA1c level means diabetes?

An HbA1c of 6.5% (48 mmol/mol) or above is the diagnostic threshold for diabetes. HbA1c between 5.7% and 6.4% (39–47 mmol/mol) indicates prediabetes — a state of increased risk where lifestyle intervention can significantly reduce progression to type 2 diabetes.

Q: How do I convert HbA1c to average blood sugar?

The ADAG (A1c-Derived Average Glucose) study established a validated formula: estimated average glucose (eAG) in mmol/L = 1.5944 × HbA1c (%) − 2.5944. For example, an HbA1c of 7.0% corresponds to an eAG of approximately 8.6 mmol/L (154 mg/dL). Use the calculator above for instant conversion.

Q: Why do some countries use mg/dL and others use mmol/L?

It is a historical difference. The United States, along with a handful of other countries, uses the older mass-concentration unit (mg/dL). Most of the world — including Australia, the UK, Canada and Europe — uses the SI unit mmol/L, which measures molar concentration. Both measure the same thing; the conversion factor for glucose is 18.02 (1 mmol/L = 18.02 mg/dL).

Q: What is the difference between HbA1c % and mmol/mol (IFCC)?

Both express the same measurement — the proportion of haemoglobin that is glycated. The older NGSP/DCCT method reports HbA1c as a percentage (e.g. 6.5%). The newer IFCC method reports in mmol/mol (e.g. 48 mmol/mol). Australia reports both on pathology results. The conversion is: IFCC (mmol/mol) = 10.93 × NGSP (%) − 23.50.

Q: When is HbA1c unreliable?

HbA1c depends on a normal red-cell lifespan (~120 days). It can be falsely low in haemolytic anaemia, significant blood loss, or haemoglobinopathies (e.g. thalassaemia, sickle cell disease), and falsely high in iron-deficiency anaemia or chronic kidney disease. Pregnancy and recent transfusion also affect accuracy. In these situations, fructosamine or CGM-derived glucose data may be more reliable.

Q: What is an oral glucose tolerance test (OGTT)?

An OGTT involves drinking a standardised 75 g glucose solution after an overnight fast, then measuring blood glucose at 2 hours. It is the gold standard for diagnosing impaired glucose tolerance and is commonly used in pregnancy to screen for gestational diabetes. A 2-hour glucose below 7.8 mmol/L (140 mg/dL) is normal; 7.8–11.0 mmol/L (140–199 mg/dL) indicates impaired glucose tolerance; and ≥11.1 mmol/L (200 mg/dL) indicates diabetes.

Convert blood glucose between mmol/L (Australia, Europe) and mg/dL (United States), and translate HbA1c into estimated average glucose (eAG) and IFCC units — instantly. Diagnostic reference ranges for fasting glucose, OGTT and HbA1c are shown below.

Blood Glucose

mmol/L

mg/dL

1 mmol/L = 18.02 mg/dL · applies to fasting, random and OGTT glucose

HbA1c ↔ Estimated Average Glucose

HbA1c (%)

eAG (mmol/L)

ADAG formula: eAG (mmol/L) = 1.5944 × HbA1c (%) − 2.5944 · also: eAG — mg/dL · IFCC — mmol/mol

When HbA1c may be unreliable: conditions that affect red-cell turnover — haemoglobinopathies (e.g. thalassaemia trait), iron-deficiency anaemia, recent transfusion, chronic kidney disease and pregnancy. In these settings fructosamine or continuous glucose monitoring may be more appropriate.

Reference Ranges — Fasting Glucose, OGTT & HbA1c

Commonly used diagnostic thresholds for non-pregnant adults. Fasting glucose thresholds follow ADA criteria; WHO criteria define impaired fasting glucose at a slightly higher cutoff of 6.1–6.9 mmol/L (110–125 mg/dL).

Fasting Plasma Glucose

Category	mmol/L	mg/dL	Status
Normal	<5.6	<100	Normal
Impaired fasting glucose	5.6–6.9	100–125	Prediabetes
Diabetes	≥7.0	≥126	Diabetes

2-Hour Oral Glucose Tolerance Test (OGTT)

Category	mmol/L	mg/dL	Status
Normal	<7.8	<140	Normal
Impaired glucose tolerance	7.8–11.0	140–199	Prediabetes
Diabetes	≥11.1	≥200	Diabetes

HbA1c

Category	HbA1c (%)	IFCC (mmol/mol)	Status
Normal	<5.7	<39	Normal
Prediabetes	5.7–6.4	39–47	Prediabetes
Diabetes	≥6.5	≥48	Diabetes

Important: a single abnormal result is generally not sufficient to diagnose diabetes — confirmation with a repeat test on a separate day is usually required, unless there is unequivocal hyperglycaemia with classic symptoms (polyuria, polydipsia, unexplained weight loss). Gestational diabetes has different thresholds; see RANZCOG guidelines for Australian criteria.

Frequently Asked Questions

What is a normal fasting blood sugar level?

A normal fasting blood glucose level is below 5.6 mmol/L (100 mg/dL). Levels between 5.6 and 6.9 mmol/L (100–125 mg/dL) are classified as impaired fasting glucose (prediabetes), and a fasting glucose of 7.0 mmol/L (126 mg/dL) or above suggests diabetes. This should be confirmed with a repeat test.

What HbA1c level means diabetes?

An HbA1c of 6.5% (48 mmol/mol) or above is the diagnostic threshold for diabetes. HbA1c between 5.7% and 6.4% (39–47 mmol/mol) indicates prediabetes — a state of increased risk where lifestyle intervention can significantly reduce progression to type 2 diabetes.

How do I convert HbA1c to average blood sugar?

The ADAG (A1c-Derived Average Glucose) study established a validated formula: estimated average glucose (eAG) in mmol/L = 1.5944 × HbA1c (%) − 2.5944. For example, an HbA1c of 7.0% corresponds to an eAG of approximately 8.6 mmol/L (154 mg/dL). Use the calculator above for instant conversion.

Why do some countries use mg/dL and others use mmol/L?

It is a historical difference. The United States, along with a handful of other countries, uses the older mass-concentration unit (mg/dL). Most of the world — including Australia, the UK, Canada and Europe — uses the SI unit mmol/L, which measures molar concentration. Both measure the same thing; the conversion factor for glucose is 18.02 (1 mmol/L = 18.02 mg/dL).

What is the difference between HbA1c % and mmol/mol (IFCC)?

Both express the same measurement — the proportion of haemoglobin that is glycated. The older NGSP/DCCT method reports HbA1c as a percentage (e.g. 6.5%). The newer IFCC method reports in mmol/mol (e.g. 48 mmol/mol). Australia reports both on pathology results. The conversion is: IFCC (mmol/mol) = 10.93 × NGSP (%) − 23.50.

When is HbA1c unreliable?

HbA1c depends on a normal red-cell lifespan (~120 days). It can be falsely low in haemolytic anaemia, significant blood loss, or haemoglobinopathies (e.g. thalassaemia, sickle cell disease), and falsely high in iron-deficiency anaemia or chronic kidney disease. Pregnancy and recent transfusion also affect accuracy. In these situations, fructosamine or CGM-derived glucose data may be more reliable.

What is an oral glucose tolerance test (OGTT)?

An OGTT involves drinking a standardised 75 g glucose solution after an overnight fast, then measuring blood glucose at 2 hours. It is the gold standard for diagnosing impaired glucose tolerance and is commonly used in pregnancy to screen for gestational diabetes. A 2-hour glucose below 7.8 mmol/L (140 mg/dL) is normal; 7.8–11.0 mmol/L (140–199 mg/dL) indicates impaired glucose tolerance; and ≥11.1 mmol/L (200 mg/dL) indicates diabetes.

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