A1C Calculator: Convert A1C to Average Blood Sugar (eAG)

Your A1C test result tells you one number, but the number your doctor actually talks to you about — the one that maps to your day-to-day blood sugar readings — is estimated average glucose (eAG). This free A1C calculator converts your A1C percentage into eAG in both mg/dL and mmol/L instantly, and it works in reverse too, so you can convert an average glucose reading back into an estimated A1C. Enter a number below to get started, or scroll down for the full conversion chart, the diagnostic ranges the American Diabetes Association (ADA) uses, and answers to the most common questions about what these numbers mean.

What Is A1C and Why Does It Get Converted to eAG?

A1C (also called HbA1c or hemoglobin A1c) is a blood test that measures the percentage of your hemoglobin that has glucose attached to it. Because red blood cells live for about three months, the A1C result reflects your average blood sugar over roughly the past 2–3 months — not a single moment, the way a finger-stick or continuous glucose monitor (CGM) reading does.

The problem is that a percentage like "7.2%" doesn't mean much to most people, because it isn't measured in the same units as the glucose readings from a meter or CGM. That's where estimated average glucose (eAG) comes in. eAG translates the A1C percentage into the same mg/dL (or mmol/L) units your glucose meter already uses, so you can compare the two directly. The ADA adopted this eAG conversion in 2008 specifically so patients could understand their A1C in familiar terms.

A1C to eAG Conversion Chart

The table below uses the same formula built into the calculator above, rounded the way the ADA rounds its own published conversion table.

ADA Diagnostic Ranges for A1C

These are the standard diagnostic categories published by the American Diabetes Association. They're educational reference points only — a diagnosis always requires a clinician interpreting your specific lab result, sometimes alongside a second confirmatory test.

If your number falls in the prediabetes range, our guide on prediabetes symptoms and what to eat to help reverse it covers the next steps most clinicians recommend before medication is on the table.

How This Calculator Works

This tool uses the official ADA/NGSP-endorsed conversion formula from the landmark ADAG (A1c-Derived Average Glucose) Study:

This same formula, run in reverse, converts an average glucose reading back into an estimated A1C. To convert between mg/dL and mmol/L, we divide (or multiply) by 18.016, the standard molar mass conversion for glucose.

The formula comes from Nathan DM, et al., "Translating the A1C Assay Into Estimated Average Glucose Values," published in Diabetes Care (2008;31(8):1473–1478) — the study the ADA itself cites for its own official eAG calculator. We did not estimate or simplify this formula; it is reproduced exactly as published and as used in ADA patient materials.

A1C vs. eAG vs. a Glucose Meter or CGM Reading — What's the Difference?

These three numbers all describe blood sugar, but they answer different questions:

A1C is a lab test reflecting your average blood sugar over about 2–3 months. It's typically drawn every 3–6 months and is the number your doctor uses to diagnose prediabetes/diabetes and judge long-term control.

eAG is not a separate test — it's simply your A1C result translated into the mg/dL or mmol/L units your meter uses, so the long-term number becomes easier to compare against your daily readings.

A glucose meter or CGM reading is a snapshot of your blood sugar at one moment (or, for a CGM, a continuous stream of moments). A single reading can swing widely around your true eAG depending on meals, activity, stress, and sleep — which is exactly why A1C/eAG exists as a longer-term average to smooth all of that out.

How Often Should You Get an A1C Test?

For most adults without diabetes, the ADA and CDC recommend A1C screening starting at age 35, then every 1–3 years if the result is normal (sooner if you're overweight and have another risk factor, such as a family history of diabetes, high blood pressure, or a history of gestational diabetes). If you've already been diagnosed with prediabetes, most clinicians recheck A1C annually. If you have diabetes, the general guidance is every 3–6 months, more often if your treatment plan recently changed or your readings are unstable.

None of these intervals are a substitute for your own doctor's recommendation — they're general population guidance, and your personal risk factors (family history, weight, blood pressure, prior gestational diabetes, ethnicity-linked risk, PCOS, and others) can shift how often testing makes sense for you specifically.

What Can Throw Off an A1C Reading?

Because A1C is a proxy measurement (it looks at glucose bound to hemoglobin, not glucose in your blood directly), a handful of conditions can make the number read higher or lower than your true average blood sugar:

Anemia and blood loss. Recent blood loss, hemolytic anemia, or conditions that shorten red blood cell lifespan can lower A1C artificially, since the cells don't live long enough to accumulate as much glucose.

Hemoglobin variants. Certain inherited hemoglobin variants (such as sickle cell trait) can interfere with some A1C lab methods, leading to falsely high or low results depending on the assay used. If you know you carry one of these variants, tell your doctor — they may use a different test method or rely more on direct glucose monitoring.

Kidney disease and iron deficiency. Both can push A1C higher than your actual average glucose would suggest.

Recent transfusion or pregnancy. Both can temporarily distort A1C's relationship to true average glucose.

This is exactly why eAG and A1C are meant to be read together with context from your doctor, not used as a stand-alone diagnostic in isolation — and it's also why this calculator, like the ADA's own version, is explicitly framed as an educational conversion tool rather than a diagnostic instrument.

How to Read Your Lab Report Using This Tool

Most lab reports list your A1C as a single percentage (for example, "A1C: 6.1%"), sometimes with a reference range printed alongside it. To make sense of that number in the same units your glucose meter uses:

1. Take the percentage exactly as printed on your lab report — don't round it further than the lab already has.

2. Enter it into the "A1C → Average Blood Sugar" calculator above.

3. Compare the resulting eAG (in mg/dL or mmol/L, whichever matches your glucose meter) against your own logged meter or CGM averages for a sanity check — they won't match exactly, but they should be in the same neighborhood.

4. Note which diagnostic range (normal, prediabetes, diabetes) the result falls into, and bring any questions to your next appointment rather than trying to self-diagnose from the category alone.

Frequently Asked Questions

Is this A1C calculator accurate?
The math is exact — it's the same published ADA/NGSP formula used in clinical patient materials. What can vary slightly is your actual lab A1C itself, which depends on the lab's testing method and, in rare cases, conditions like anemia or certain hemoglobin variants that can skew an A1C reading independent of blood sugar.

Can I use this calculator instead of getting an A1C blood test?
No. This tool only converts between two ways of expressing a result you already have (or a value you want to translate). It cannot measure your blood sugar and does not replace a lab test.

What A1C is considered prediabetes?
The ADA defines prediabetes as an A1C of 5.7% to 6.4%. If your result falls in this range, see our detailed guide on prediabetes symptoms for what typically happens next.

What A1C is considered diabetes?
6.5% or higher on two separate tests (or one test plus symptoms/other confirming labs), per ADA diagnostic criteria.

Why does my glucose meter show different numbers than my eAG suggests?
Your meter reading is a single moment in time, while eAG is a 2–3 month average. A morning fasting reading, a post-meal spike, and an average glucose (eAG) figure can all look quite different from each other and still be entirely consistent.

Does losing weight or changing diet lower A1C?
For many people with prediabetes, yes — the ADA and CDC both note that modest weight loss (around 5–7%) combined with dietary changes can meaningfully reduce A1C and lower the risk of progressing to type 2 diabetes. Our prediabetes diet guide covers the specific changes with the most evidence behind them.

Is eAG the same as "average blood sugar" on my glucose meter's app?
Not necessarily. Many meter and CGM apps calculate their own "average glucose" directly from your logged readings over a period you choose (7, 14, 30, 90 days), which can differ from the eAG derived from your lab A1C, especially if your logged readings don't cover a full 24 hours a day.