How to use A1C Calculator
The A1C calculator converts between A1C percentage and estimated Average Glucose (eAG) using the ADAG (A1C-Derived Average Glucose) formula: eAG (mg/dL) = 28.7 × A1C − 46.7. Results are displayed in both mg/dL and mmol/L. The reverse direction is also supported: enter any average glucose value to calculate the corresponding A1C. A1C reflects the cumulative glycation of haemoglobin over the prior 2–3 months and is the primary long-term blood glucose monitoring metric for diabetes management.
- Select your conversion direction:"A1C → Average Glucose" or "Average Glucose → A1C".
- If converting from average glucose, also choose your unit (mg/dL or mmol/L).
- Enter your A1C percentage (e.g. 6.5) or your average glucose value.
- Click Convert to see the result in both A1C% and glucose (mg/dL and mmol/L).
- Review the reference table showing common A1C values, categories and average glucose equivalents.
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The ADAG formula and why it matters
The ADAG study (2008) enrolled 507 participants across 10 countries and correlated laboratory A1C values with continuous glucose monitoring data averaged over 3 months. The resulting linear equation — eAG (mg/dL) = 28.7 × A1C − 46.7 — is the standard formula endorsed by the ADA, EASD and IDF. Prior to ADAG, clinicians used a less accurate older formula; the newer equation better reflects glucose levels experienced by diverse populations and is now the basis for A1C reporting by most clinical laboratories.
| A1C (%) | Category | eAG (mg/dL) | eAG (mmol/L) |
|---|---|---|---|
| < 5.7% | Normal | < 117 | < 6.5 |
| 5.7–6.4% | Prediabetes | 117–137 | 6.5–7.6 |
| 6.5%+ | Diabetes (threshold) | 140+ | 7.8+ |
| 7.0% | ADA target for most adults | 154 | 8.6 |
| 8.0% | Above ADA target | 183 | 10.2 |
Limitations of A1C as a glucose marker
A1C reflects a weighted average of glucose over ~3 months, but the most recent 4–6 weeks contribute more heavily than earlier weeks because newer red blood cells are more abundant. Conditions that alter red blood cell lifespan — haemolytic anaemia, haemoglobin variants (HbS, HbC), recent blood transfusion, iron deficiency — can falsely raise or lower A1C independent of glucose. In these cases, fructosamine or continuous glucose monitoring better reflects glycaemic control. Additionally, A1C cannot capture glucose variability or hypoglycaemia, which matter clinically.
Worked examples
A1C of 7%
Inputs: 28.7 × 7 − 46.7
Result: ≈ 154 mg/dL (8.6 mmol/L) estimated average glucose
A1C of 5.5%
Inputs: 28.7 × 5.5 − 46.7
Result: ≈ 111 mg/dL (6.2 mmol/L) — normal range
Glossary
- A1C (HbA1c)
- Glycated haemoglobin — the percentage of haemoglobin with glucose attached, reflecting ~3 months of blood sugar.
- eAG
- Estimated Average Glucose — the blood glucose average equivalent to a given A1C, calculated by the ADAG formula.
- ADAG
- A1C-Derived Average Glucose — the 2008 international study establishing the standard A1C-to-eAG conversion formula.
- mmol/L
- Millimoles per litre — the glucose unit used in most countries outside the US; 1 mmol/L ≈ 18 mg/dL.
- Haemoglobin variant
- An abnormal haemoglobin structure (e.g. HbS in sickle cell trait) that can falsify A1C readings.
Related reading
Frequently Asked Questions
Why use A1C Calculator?
- Converts between A1C percentage and eAG using the ADAG formula endorsed by ADA, EASD and IDF
- Displays glucose results in both mg/dL and mmol/L to match any country's standard reporting unit
- Supports the reverse calculation — enter average glucose to find the corresponding A1C percentage
- Includes a reference table with ADA diagnostic categories from Normal through Diabetes
Common use cases
- Translate a lab A1C result into an average glucose figure to make the number more interpretable
- Convert mmol/L glucose readings to mg/dL when comparing results from labs in different countries
- Identify where a given A1C falls relative to the 6.5% diabetes diagnostic threshold
- Track progress toward an A1C reduction target by entering current average glucose readings over time
- Verify a glucose-to-A1C conversion before discussing lab results with a healthcare provider
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