HbA1c Calculator
Convert between HbA1c (%) and estimated average glucose (eAG) using the validated ADAG formula. Enter your A1c to see average glucose — or enter average glucose to estimate A1c. Supports mg/dL and mmol/L. Educational reference only.
🔬 A1c ↔ Average Glucose Converter
Result
mg/dL
mmol/L
%
Category
A1c Reference Table (ADA 2024)
| HbA1c (%) | eAG (mg/dL) | eAG (mmol/L) | ADA Category |
|---|---|---|---|
| 5.0 | 97 | 5.4 | Normal |
| 5.7 | 117 | 6.5 | Prediabetes threshold (lower) |
| 6.4 | 137 | 7.6 | Prediabetes threshold (upper) |
| 6.5 | 140 | 7.8 | Diabetes diagnosis threshold |
| 7.0 | 154 | 8.6 | ADA target (most adults) |
| 7.5 | 169 | 9.4 | Above target — reassess regimen |
| 8.0 | 183 | 10.2 | Uncontrolled — action needed |
| 9.0 | 212 | 11.8 | Significantly elevated |
| 10.0 | 240 | 13.4 | High risk — urgent review |
Source: ADA Standards of Medical Care 2024; Nathan DM et al. ADAG Study. Diabetes Care. 2008.
ADAG Formula
The ADAG (A1c-Derived Average Glucose) formula was derived from a multi-center study correlating lab A1c with continuous glucose monitor data across ~500 patients. It replaced earlier approximations and is endorsed by ADA. The relationship is linear — each 1% A1c change ≈ 28.7 mg/dL (1.6 mmol/L) in average glucose.
A1c has known limitations. Results can be falsified by hemoglobin variants (sickle cell trait, thalassemia), hemolytic anemia, iron deficiency, and high-dose vitamin C. In these conditions, fructosamine or continuous glucose monitoring may be more reliable. Discuss with your provider if your A1c result seems inconsistent with your meter readings.
What HbA1c Actually Measures
HbA1c (glycated hemoglobin) is the share of your hemoglobin — the oxygen-carrying protein in red blood cells — that has glucose bound to it. Because red blood cells live about three months, A1c reflects your average glucose exposure over roughly the previous 8–12 weeks, weighted toward the most recent four. Unlike a finger-stick, it can't be "gamed" by a few good days before the appointment.
That long window is both its strength and its weakness: A1c is an excellent measure of overall trend, but it hides the day-to-day swings — the lows and post-meal spikes — that two people sharing the same 7.0% can experience very differently. To see your A1c as a familiar glucose number, use the A1c to Average Blood Glucose Calculator.
How Often Should HbA1c Be Tested?
The ADA's general guidance:
- Twice a year if you are meeting your treatment goals and glucose is stable.
- Every 3 months (quarterly) if your therapy has changed or you are not yet at goal.
Because the test averages months of data, checking it more often than about every three months rarely adds useful information — there simply hasn't been enough time for a meaningful change to register.
Frequently Asked Questions
What is a good HbA1c level?
The ADA target for most non-pregnant adults with diabetes is below 7%. Some people aim for below 6.5%, while a looser goal below 8% may suit older adults or those at high risk of hypoglycemia. Below 5.7% is considered normal.
How do I convert my HbA1c to average glucose?
Use the ADAG formula: eAG (mg/dL) = 28.7 × A1c − 46.7. An A1c of 7% is about 154 mg/dL (8.6 mmol/L). The calculator above does this in both directions.
How often should I get an HbA1c test?
Generally twice a year if you are at goal and stable, or every 3 months if your treatment changed or you are not yet at target. More frequent testing rarely helps because A1c reflects months of data.
Can anything make an HbA1c result inaccurate?
Yes. Hemoglobin variants (such as sickle cell trait), hemolytic or iron-deficiency anemia, recent blood loss, pregnancy, and high-dose vitamin C can skew A1c. If your result doesn't match your meter, ask your provider about CGM or fructosamine testing.
Sources
- Nathan DM et al. "Translating the A1C assay into estimated average glucose values." Diabetes Care. 2008;31(8):1473–1478.
- American Diabetes Association. Standards of Medical Care — 2024. Section 6.
Last reviewed: June 2025