Glucose and HbA1c Calculator — Unit Converter & Reference Ranges
This page lets you convert blood glucose between mmol/L and mg/dL, and translate HbA1c into estimated average glucose (eAG), with IFCC conversion included — instantly, with no buttons to click. Clinical reference ranges for fasting glucose, OGTT, and HbA1c are also provided below, based on ADA diagnostic thresholds.
Whether you’re a healthcare professional interpreting pathology results or a patient trying to make sense of your blood sugar levels, everything you need is here in one place.
Note: HbA1c may be unreliable in conditions that affect red blood cell turnover, including 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
The table below summarises commonly used diagnostic thresholds for fasting glucose, 2-hour OGTT, and HbA1c in non-pregnant adults. The fasting glucose thresholds shown 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. Diagnosis typically requires confirmation with a repeat test on a separate day, unless the patient has unequivocal hyperglycaemia with classic symptoms (polyuria, polydipsia, unexplained weight loss). Gestational diabetes has different diagnostic thresholds — refer to RANZCOG guidelines for Australian criteria.
Frequently Asked Questions
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.
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.
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.
It's 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 (Système International) unit, mmol/L, which measures molar concentration. The two systems measure the same thing; the conversion factor for glucose is 18.02 (i.e. 1 mmol/L = 18.02 mg/dL).
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.
HbA1c depends on normal red blood cell lifespan (~120 days). It can be falsely low in haemolytic anaemia, significant blood loss, or haemoglobinopathies (e.g. thalassaemia, sickle cell disease). It can be falsely high in iron deficiency anaemia or chronic kidney disease. Pregnancy and recent blood transfusion also affect accuracy. In these situations, fructosamine or CGM-derived glucose data may be more reliable.
An OGTT involves drinking a standardised 75g 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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