Use this A1c calculator to convert HbA1c to estimated average glucose and back, with mmol/L, mg/dL, IFCC mmol/mol, ADA-style range guidance, quick examples.
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A1c calculator for estimated average glucose Use this A1c calculator to convert HbA1c into estimated average glucose, compare A1c to blood sugar in mmol/L or mg/dL, or reverse the calculation when you already know an eAG result.
Input
Convert A1c and estimated average glucose
Quick examples
Mode
Result
Estimated average glucose
8.6 mmol/L
154.2 mg/dL
Diabetes — above individual target for most
A1c
7%
IFCC
53 mmol/mol
eAG step
A 1 percentage-point A1c change is roughly 28.7 mg/dL or 1.6 mmol/L of estimated average glucose.
HbA1c reflects your average blood glucose over the preceding 2–3 months. It is influenced most heavily by the most recent 4–6 weeks. An eAG of 8.6 mmol/L (154.2 mg/dL) represents an estimated daily average, not a single point-in-time reading.
CGM and GMI context CGM reports may show GMI rather than lab A1c; GMI, eAG, and lab A1c can differ when red blood cell turnover or glucose variability changes.
A1c
IFCC
mmol/L
mg/dL
Category
< 5.7%
< 39
< 6.5
< 117
Normal
5.7–6.4%
39–46
6.6–9.0
119–162
Pre-diabetes
< 7.0%
< 53
< 8.6
< 154
Diabetes target (many)
7.0–7.9%
53–63
8.6–10.1
154–183
Above target
≥ 8.0%
≥ 64
≥ 10.1
≥ 183
Significantly above target
A1c targets vary by individual clinical context. A result in the diabetes range should be confirmed by a healthcare provider and does not constitute a diagnosis on its own.
HbA1c (glycated haemoglobin) reflects average blood glucose over the preceding 2–3 months. This A1c calculator converts A1c to estimated average glucose (eAG) in both mmol/L and mg/dL, shows the IFCC mmol/mol equivalent, and reverses the conversion with the ADA-validated ADAG formula.
How to use the A1c calculator
Choose the direction that matches your question: A1c to eAG when you have a lab result, or eAG to A1c when you already know an average glucose reading. The calculator shows both mmol/L and mg/dL so you can compare the result with whichever blood sugar unit you use most often, and it adds the IFCC mmol/mol equivalent used in many laboratory reports.
The conversion is an estimate rather than a diagnosis. It is most useful for understanding how a long-term A1c result relates to day-to-day blood glucose readings, especially when you are comparing HbA1c to a glucose log, CGM summary, or estimated average glucose report.
What HbA1c measures
Haemoglobin A1c forms when glucose in the bloodstream attaches to haemoglobin in red blood cells. Since red blood cells live approximately 90–120 days, the proportion of glycated haemoglobin reflects average blood glucose over that period. Higher average glucose means more glycation and a higher A1c percentage.
A1c is weighted toward the most recent 4–6 weeks because newly formed red blood cells represent the most recently glycated fraction. A major illness, blood transfusion, or haemolytic anaemia can invalidate A1c as a measure of average glucose.
The ADAG formula
The A1c-Derived Average Glucose (ADAG) study validated the relationship between A1c and average glucose measured by continuous glucose monitoring in a diverse population. The resulting formula — eAG (mg/dL) = 28.7 × A1c% − 46.7 — superseded earlier linear estimates and is the basis of the ADA eAG reporting standard. The conversion to mmol/L is eAG (mmol/L) = 1.5944 × A1c% − 2.5944.
NGSP percent, IFCC mmol/mol, and eAG are different views of the same result
A1c is often shown as an NGSP or DCCT-aligned percentage, such as 7.0%. Some countries and laboratories also report HbA1c in IFCC units, written as mmol/mol. The units look very different even when they describe the same glycated-haemoglobin result, which is why an A1c converter that includes IFCC mmol/mol can prevent avoidable confusion.
The calculator keeps the familiar percentage as the main input, then shows the IFCC equivalent beside the estimated average glucose. For example, an A1c of 7.0% is about 53 mmol/mol and about 154 mg/dL or 8.6 mmol/L eAG. Those are translations of the same lab marker, not separate tests.
IFCC HbA1c (mmol/mol) = (A1c% - 2.15) × 10.929
This converts an NGSP/DCCT-aligned A1c percentage into IFCC mmol/mol units.
A1c% = (eAG mg/dL + 46.7) ÷ 28.7
This reverses the ADAG equation when an estimated average glucose value is entered.
Worked example: A1c 7.0%
An HbA1c of 7.0% converts to an estimated average glucose of about 8.6 mmol/L or 154 mg/dL. That is why 7.0% is often used as the familiar reference point when clinicians explain the relationship between a lab A1c result and day-to-day glucose readings.
The reverse conversion is also useful. If a glucose log or CGM summary averages around 154 mg/dL, the equivalent A1c is about 7.0%. This does not guarantee that the eventual lab A1c will be exactly 7.0%, but it gives a practical way to connect daily readings with a longer-term marker.
A one percentage-point A1c difference is roughly 28.7 mg/dL or 1.6 mmol/L of estimated average glucose. That rule of thumb makes the reference table easier to interpret: moving from 8.0% to 7.0% is not a tiny change, even though it is only one point on the A1c scale.
When A1c can be misleading
Some conditions make HbA1c less reliable. Iron deficiency anaemia, haemolytic anaemia, recent blood transfusion, haemoglobin variants, pregnancy, and some kidney disorders can all shift A1c away from the glucose average you would expect. In those cases, clinicians often lean more heavily on meter data, continuous glucose monitoring, or alternative markers such as fructosamine.
If your lab A1c does not match your home readings, the mismatch is worth reviewing clinically rather than assuming the calculator is wrong. The calculator uses the standard population formula, but individual biology can push results higher or lower than the estimate.
A1c vs CGM average glucose and GMI
A continuous glucose monitor can show a mean glucose that is close to the A1c-derived eAG, but the two values are not identical. CGM captures short-term variability, while A1c is a longer-term weighted average that cannot show spikes, lows, or the timing of excursions.
Many CGM reports also show glucose management indicator, or GMI. GMI is calculated from CGM mean glucose and is often compared with lab A1c, but it is not the same measurement. A1c depends on haemoglobin glycation and red blood cell turnover, while GMI depends on the sensor data period and the formula used by the report.
That is why this A1c to eAG calculator is best used as a translation tool. It helps you compare HbA1c, estimated average glucose, IFCC mmol/mol, and blood sugar readings without pretending that all measures tell exactly the same story.
How to use the result in a clinical conversation
The most useful next step is usually not to treat the converted number as a new diagnosis. Instead, use it to ask better questions: does the A1c match meter or CGM averages, are lows and highs hidden inside the average, and could a condition affecting red blood cells make the lab result less reliable?
For people already living with diabetes, A1c targets are individualized. Age, pregnancy, hypoglycaemia risk, kidney disease, cardiovascular disease, treatment regimen, and personal circumstances can all change the appropriate target. A calculator can translate units and show broad ranges, but the target itself should come from clinical care.
Use A1c to eAG when translating a lab HbA1c result into familiar blood sugar units.
Use eAG to A1c when a meter log or CGM average needs a rough A1c-equivalent context.
Use IFCC mmol/mol when comparing with a lab report that does not use percent units.
Review discordant A1c, CGM, and finger-stick readings with a qualified clinician.
Frequently asked questions
Is HbA1c the same as A1c?
Yes. HbA1c and A1c are commonly used to mean the same lab test, although HbA1c is the more precise biochemical term. Both refer to glycated haemoglobin and both are used to estimate average blood glucose over the previous 2–3 months.
What is a normal A1c?
A commonly used normal range is below 5.7%. An A1c of 5.7–6.4% is often called pre-diabetes, and 6.5% or above is typically in the diabetes range. Targets for people already living with diabetes may be different and should be set individually.
How often should A1c be tested?
For people with well-controlled diabetes meeting treatment targets, the ADA recommends testing at least twice per year. For people with poorly controlled diabetes or those whose therapy has changed, quarterly testing is recommended. For people without diabetes but with risk factors, testing frequency depends on clinical context.
Can this calculator diagnose diabetes?
No. The calculator converts between A1c and estimated average glucose, but a diagnosis depends on the full clinical picture and may require repeat testing, symptoms, or other laboratory confirmation. Use the result as context, not as a stand-alone diagnosis.
Can A1c be falsely high or low?
Yes. Conditions that increase red blood cell lifespan (iron deficiency anaemia, hypothyroidism) can falsely elevate A1c. Conditions that decrease red blood cell lifespan (haemolytic anaemia, sickle cell disease, recent blood transfusion) can falsely lower it. In these cases, other measures such as fructosamine or continuous glucose monitoring are preferred.
Why can eAG differ from my CGM average?
eAG is a population-based estimate derived from the ADAG study. Your CGM average reflects the exact readings recorded during the period you wore the sensor, while eAG is inferred from A1c and weighted toward the most recent 4–6 weeks.
What is A1c in mmol/mol?
A1c in mmol/mol is the IFCC reporting unit for HbA1c. It expresses the same glycated-haemoglobin result in a different unit system. For example, an A1c of 7.0% is about 53 mmol/mol.
How do I convert A1c to average blood sugar?
Use the ADAG equation: eAG in mg/dL = 28.7 × A1c% − 46.7. To show the result in mmol/L, divide mg/dL by about 18 or use the equivalent formula eAG in mmol/L = 1.5944 × A1c% − 2.5944.
Is GMI the same as A1c?
No. GMI is calculated from continuous glucose monitor data, while lab A1c is measured from glycated haemoglobin in blood. They often point in the same direction, but they can differ because they rely on different data and different biology.
Why does the calculator show both mmol/L and mg/dL?
Different countries and devices use different glucose units. Showing both mmol/L and mg/dL lets the same A1c calculator work for people comparing lab reports, glucose meters, CGM summaries, and clinical notes across unit systems.
