A1C Calculator (HbA1c to eAG)

Convert A1C to estimated average glucose and back, in mg/dL or mmol/L. Uses the ADAG study formula — the equation labs and the ADA use — with your result classified against the current diagnostic thresholds.

Estimated average glucose (eAG) converts A1C into the same mg/dL or mmol/L units as a glucose meter, using eAG = 28.7 × A1C − 46.7. An A1C below 5.7% is normal, 5.7–6.4% is prediabetes, and 6.5% or above (confirmed) is diabetes, per ADA criteria.

ADAG study formula (Nathan et al., 2008) Runs in your browser — nothing sent Medically reviewed
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Formula: eAG (mg/dL) = 28.7 × A1C − 46.7 — the ADAG study equation (Nathan et al., Diabetes Care, 2008), the basis for the ADA's own eAG calculator.

Does your A1C result vary for you?

A1C-to-glucose conversion uses one formula for everyone — but whether the A1C number itself is trustworthy depends on things the formula can't see.

DirectionChanges the math
The ADAG formula runs both ways: eAG = 28.7 × A1C − 46.7, or A1C = (eAG + 46.7) / 28.7. Use the toggle above to switch — the calculator applies whichever equation matches the value you actually have.
UnitsChanges the math
Average glucose can be entered in mg/dL (US) or mmol/L (UK, EU, most of the world) — the calculator converts automatically (mmol/L × 18 = mg/dL) before applying the formula, and shows the result in both.
Medical conditionsChanges reliability
A1C reflects glucose bound to hemoglobin over a red blood cell's ~3-month lifespan. Anemia, hemoglobin variants (e.g. sickle cell trait), chronic kidney disease, pregnancy, and recent blood loss or transfusion all change red blood cell turnover — and can make A1C read falsely high or low regardless of actual glucose. The formula can't detect this; only your clinician, with your full history, can.

How A1C-to-glucose conversion is calculated

A1C and average glucose are measured in different units for a historical reason — A1C is a percentage of glycated hemoglobin, glucose is a concentration. The ADAG study built the bridge between them.

ADAG formula (estimated average glucose)
eAG (mg/dL) = 28.7 × A1C − 46.7
Reverse: A1C = (eAG + 46.7) / 28.7 · mmol/L = mg/dL ÷ 18

The formula comes from the ADAG (A1c-Derived Average Glucose) study — Nathan et al., Diabetes Care, 2008 — which fitted A1C against continuous glucose monitor and frequent self-monitoring data from over 500 people across 10 international centers, then published the linear relationship above. It's the same formula the American Diabetes Association uses for its own eAG conversion, and the one most clinical calculators cite.

It's a population-average relationship, not a personal one. Two people with an identical A1C of 7.0% both map to an eAG of roughly 154 mg/dL — but their actual day-to-day glucose patterns, measured on a CGM, can look quite different (one steady, one with wide swings that average out to the same number). eAG tells you what glucose level would typically produce your A1C; it doesn't replace direct glucose monitoring if you need to see the pattern, not just the average.

A1C to average glucose — full reference chart

Every value below is computed with the same ADAG formula the calculator uses above, so you can look up a result without retyping it.

A1CeAG (mg/dL)eAG (mmol/L)Category
5.0%975.4Normal
5.5%1116.2Normal
6.0%1257.0Prediabetes
6.5%1407.8Diabetes
7.0%1548.6Diabetes
7.5%1699.4Diabetes
8.0%18310.2Diabetes
8.5%19711.0Diabetes
9.0%21211.8Diabetes
9.5%22612.6Diabetes
10.0%24013.4Diabetes
11.0%26914.9Diabetes
12.0%29816.5Diabetes
13.0%32618.1Diabetes
14.0%35519.7Diabetes
A single reading is not the same as eAG
eAG describes a true 2-3 month average, not one fasting or random glucose reading. Plugging a single meter reading into this formula (a common mix-up — "what's my A1C if my blood sugar is 110?") gives a misleading answer, because one reading isn't your average. Fasting glucose has its own, separate ADA diagnostic thresholds: under 100 mg/dL is normal, 100-125 mg/dL is prediabetes, 126 mg/dL or above (confirmed) is diabetes.

Frequently asked questions

How do I calculate my A1C from average blood sugar?
You don't calculate A1C by hand from a glucose reading — it's measured directly from a blood sample. But you can estimate the relationship using the ADAG formula: A1C = (average glucose in mg/dL + 46.7) / 28.7. This only works for a true 2-3 month average, not a single reading — use the "Average Glucose → A1C" toggle above.
What is my A1C if my blood sugar is 110?
Depends what "110" means. A single fasting glucose reading of 110 mg/dL doesn't plug into the eAG formula, because eAG is a 2-3 month average, not one measurement. If 110 mg/dL is genuinely your average over that period (e.g. from CGM data), estimated A1C works out to about 5.5%. A single 110 mg/dL fasting reading, on its own, falls in the ADA's 100-125 mg/dL prediabetes range for fasting glucose — a separate diagnostic criterion from A1C.
What is a normal A1C level?
The ADA classifies A1C below 5.7% as normal, 5.7-6.4% as prediabetes, and 6.5% or above (confirmed on a second test) as diabetes. There's no separate "optimal" target below the normal cutoff for people without diabetes — under 5.7% is the reference range itself.
Can walking 30 minutes a day lower A1C?
Yes, for most people with elevated glucose. A meta-analysis of structured exercise trials in type 2 diabetes (Boule et al., JAMA, 2001) found an average A1C reduction of about 0.66 percentage points with regular aerobic and resistance exercise, independent of weight loss. Effects build over 8-12+ weeks of consistent activity, not days — the ADA's Standards of Care recommends at least 150 minutes of moderate activity per week partly for this reason.
Does drinking water lower A1C?
There's no direct evidence that water intake lowers A1C. Dehydration can temporarily concentrate blood glucose and skew a single glucose meter reading, but A1C reflects roughly 3 months of average glycation and isn't meaningfully moved by short-term hydration. Diet composition, physical activity and, where indicated, medication are what actually shift the 3-month average this test measures.
What makes an A1C result inaccurate?
A1C measures glucose bound to hemoglobin over a red blood cell's roughly 3-month lifespan, so anything that changes red blood cell turnover throws it off independent of actual glucose control. The ADA's Standards of Care flags iron-deficiency and hemolytic anemia, sickle cell trait and other hemoglobin variants, chronic kidney disease, pregnancy, and recent blood transfusion or loss as conditions where A1C can read falsely high or low. In these cases, fasting glucose or CGM data is more reliable than A1C.
Is eAG the same as the average on my glucose meter or CGM?
Not exactly. eAG is a statistical estimate derived from your A1C via the ADAG formula, not a direct measurement. Your actual meter or CGM average over the same period can differ, especially if your glucose swings widely day to day — two people with the same A1C can have very different glucose variability. Where you have real CGM data, that's the more precise number; eAG is what you'd expect A1C to imply, on average, across the population the ADAG study was built from.

References & Guidelines

Note: This calculator is for informational purposes and does not replace medical advice or a diagnostic test. eAG is a population-average estimate, not a personal measurement, and A1C itself can be unreliable in anemia, hemoglobin variants, chronic kidney disease, pregnancy, and after recent blood loss or transfusion. Always interpret your result alongside the reference range and any notes on your own lab report, and discuss any concern with a clinician who has your full history.

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