A1C Calculator
Convert an A1C percentage into estimated average glucose — or go the other direction — using the ADAG relationship the ADA publishes: eAG (mg/dL) = 28.7 × A1C − 46.7. Results appear in both mg/dL and mmol/L alongside the standard interpretation ranges. Informational only; it is not a diagnosis.
This tool is for education, not diagnosis. It performs a published unit conversion and nothing more. It cannot diagnose any condition, assess your individual risk, or tell you what your A1C should be — appropriate targets vary considerably between people. Discuss any result, and any change to medication, diet or monitoring, with a qualified healthcare professional who knows your history.
| A1C | |
| eAG (mg/dL) | |
| eAG (mmol/L) | |
| ADA category |
Two ways of describing the same three months
A1C and average glucose measure the same underlying thing in incompatible units, which is the whole reason this conversion exists. A1C reports the percentage of haemoglobin carrying attached glucose — a structural record accumulated over the roughly three-month lifespan of red blood cells. A meter reports millimoles or milligrams of glucose in blood right now. One is a slow photograph, the other a snapshot, and people are asked to hold both in mind simultaneously.
Estimated average glucose bridges them by restating A1C in meter units. It comes from the international ADAG study, which measured both quantities in the same participants and fitted a line through the relationship. That origin matters for interpretation: the equation describes a population average, so an individual's true average can sit somewhat above or below the converted figure. The conversion is genuinely useful for making an abstract percentage tangible — and genuinely limited as a statement about any one person.
How to use the A1C calculator
- Choose the direction. Convert an A1C percentage into estimated average glucose, or convert a known average glucose back into the equivalent A1C.
- Pick your glucose unit. mg/dL is standard in the United States; mmol/L is used across most of Europe, the Gulf and Commonwealth countries. The tool shows both regardless.
- Enter the value from your lab report. Use the figure as reported. Do not average several readings yourself — the conversion already represents an average across roughly three months.
- Read the eAG result. Estimated average glucose expresses A1C in the same units as a meter reading, which makes the two far easier to reason about together.
- Note the range context. The tool indicates which ADA category the A1C falls in. Categories are population criteria, not a diagnosis of any individual.
- Take the numbers to your clinician. A conversion is arithmetic; targets are clinical and personal. Age, pregnancy, hypoglycaemia risk and other conditions all change what an appropriate A1C is for a given person.
Key formulas
- A1C to eAG: eAG (mg/dL) = 28.7 × A1C(%) − 46.7
- eAG to A1C: A1C(%) = (eAG + 46.7) ÷ 28.7
- Unit conversion: mmol/L = mg/dL × 0.0555
Worked example
An A1C of 7.0% converts to 28.7 × 7.0 − 46.7 = 154.2 mg/dL, which is 8.56 mmol/L. Running the conversion the other way, an average glucose of 126 mg/dL gives (126 + 46.7) ÷ 28.7 = 6.02%. The relationship is a straight line, which is why every 1% of A1C corresponds to roughly 28.7 mg/dL of average glucose.
A1C to eAG reference
| A1C | eAG (mg/dL) | eAG (mmol/L) | ADA category |
|---|---|---|---|
| 5.0% | 96.8 | 5.37 | Normal |
| 5.7% | 116.9 | 6.49 | Prediabetes threshold |
| 6.5% | 139.9 | 7.76 | Diabetes threshold |
| 7.0% | 154.2 | 8.56 | Common treatment target |
| 8.0% | 182.9 | 10.15 | Above typical target |
| 9.0% | 211.6 | 11.74 | Above typical target |
Categories are ADA population criteria for interpretation, not individual targets. Personal targets are set by a clinician.
Things to keep in mind
- The equation is a population average. Individual glycation rates vary, so a personal average can differ from the converted figure.
- Some conditions distort A1C. Anaemia, recent blood loss, pregnancy, kidney or liver disease and haemoglobin variants all affect its reliability.
- Testing more often than quarterly adds little. The measurement averages over the red-cell lifespan; it cannot move faster.
- Targets are individual. Age, hypoglycaemia risk and other conditions legitimately move an appropriate target up or down.
- A converted number is not a diagnosis. Only a clinician, with your full picture, can interpret what a result means for you.
Frequently asked questions
What does A1C measure?
A1C, or glycated haemoglobin, is the percentage of haemoglobin in the blood that has glucose attached to it. Because red blood cells live roughly three months, that percentage reflects average blood glucose over that window rather than the moment of the test. It is why an A1C cannot be improved by fasting the night before — the measurement is structural, accumulated over weeks.
How is estimated average glucose calculated from A1C?
Using the relationship eAG (mg/dL) = 28.7 × A1C − 46.7, established by the international A1C-Derived Average Glucose study and adopted by the American Diabetes Association. Multiplying mg/dL by 0.0555 converts to mmol/L. The equation is a population regression: it describes the average relationship across many people, and individual variation around it is real.
What are the ADA A1C ranges?
Below 5.7% is considered normal, 5.7% to 6.4% is the prediabetes range, and 6.5% or above meets the diagnostic threshold for diabetes. Many adults with diabetes are given a treatment target near 7%, though clinicians routinely set higher or lower individual targets depending on age, other conditions and hypoglycaemia risk. Diagnosis is never made on a single number by a calculator.
Why does my meter average differ from my A1C-derived eAG?
Several ordinary reasons. Meter readings are a sample, usually taken at convenient times rather than uniformly across the day and night, so they under-represent overnight and post-meal periods. The eAG equation is also a population average, and individuals glycate haemoglobin at somewhat different rates. Discrepancies are common and are a topic for your clinician rather than evidence that one measurement is broken.
Can conditions other than diabetes affect A1C accuracy?
Yes, and meaningfully. Anything altering red blood cell lifespan can distort the result: anaemias, recent significant blood loss or transfusion, chronic kidney or liver disease, pregnancy, and certain haemoglobin variants which are common in some populations. In these situations clinicians may rely on fructosamine, continuous glucose monitoring or direct glucose testing instead. This is one of several reasons A1C interpretation belongs with a professional.
How often should A1C be tested?
Common clinical practice is roughly twice yearly when glucose is stable and at target, and about every three months when treatment has changed or control is not at target. Testing more frequently than every three months rarely adds information, because the measurement itself averages over that same period — the red cells simply have not turned over enough for a new number to mean anything different.
Last updated: 24 July 2026