A1C Conversion Calculator

How to use this A1C converter

1. Type any one value. Enter your A1C as a percent, your estimated average glucose in mg/dL or mmol/L, or your A1C in IFCC mmol/mol units — the other three fields update the instant you type. There's no "Calculate" button; the conversion is live.
2. Read your ADA category. The result card classifies your A1C against the American Diabetes Association's bands: Normal (under 5.7%), Prediabetes (5.7–6.4%), and Diabetes range (6.5% and above). The card's color and label tell you where the number lands.
3. Wearing a CGM? Use the GMI panel. Enter the average glucose your Dexcom or FreeStyle Libre reports to get your Glucose Management Indicator — the modern, CGM-based estimate of A1C. If you've also entered a lab A1C above, the tool shows the "glucose gap" between the two.
4. A1C unreliable? Use the fructosamine panel. If you have anemia, a hemoglobin variant, are pregnant, or have kidney disease, A1C can mislead. Enter a fructosamine result for an approximate A1C reflecting the last 2–3 weeks.
5. Save and share. Save each A1C reading to an on-device log to watch the trend across lab visits, export a clinician-ready PDF, or copy a share link that reopens with your exact numbers.

Why this A1C calculator is different

Almost every A1C tool online does one thing: convert A1C to estimated average glucose, in one direction, with a button. The official ADA calculator does exactly that and nothing more. Here's what this one adds:

• Four representations, both directions, no button. A1C (%), eAG in mg/dL, eAG in mmol/L, and IFCC mmol/mol all live in one engine — type any field and the rest follow. Most calculators show two of these at best, and only one direction.
• GMI for the CGM era. If you wear a continuous glucose monitor, your "average glucose" is not the same thing as a lab A1C — the Glucose Management Indicator (GMI) is the formula built specifically for sensor data. No other A1C converter on the first page of Google includes it.
• Fructosamine, for when A1C lies. A1C assumes normal red-blood-cell lifespan. In anemia, hemoglobinopathies, recent transfusion, pregnancy, and chronic kidney disease, that assumption breaks and A1C can read falsely high or low. A fructosamine sidesteps the problem — and this tool estimates the A1C-equivalent.
• Honest about uncertainty. GMI and fructosamine conversions are labeled as approximate, because they are. The tool tells you when two markers disagree instead of hiding it behind a single tidy number.
• Reviewed by a named physician, with the math shown. Every formula is printed below with its peer-reviewed source. Most calculator pages are anonymous; this one is reviewed by Dr. David Taylor, MD, PhD.
• Free to embed. Diabetes educators, primary-care practices, and patient-education sites can drop this calculator onto their own pages with one line of code — attribution included, no fee, no signup.

How this calculator works (the math)

Every conversion runs client-side. No data leaves your browser, and nothing is stored on a server.

A1C ↔ estimated average glucose (eAG)

The relationship between A1C and average glucose comes from the 2008 A1c-Derived Average Glucose (ADAG) study, which paired months of continuous and self-monitored glucose with lab A1C across hundreds of participants:

eAG (mg/dL) = 28.7 × A1C(%) − 46.7

A1C (%) = (eAG mg/dL + 46.7) ÷ 28.7

To switch glucose units, mg/dL is divided by 18 (the molar conversion for glucose): eAG (mmol/L) = eAG (mg/dL) ÷ 18. This reproduces the American Diabetes Association's published eAG table exactly — A1C 6% → 126 mg/dL (7.0 mmol/L), 7% → 154 mg/dL (8.6 mmol/L), 8% → 183 mg/dL (10.2 mmol/L). Per Nathan DM et al., Diabetes Care 2008;31(8):1473–8.

NGSP (%) ↔ IFCC (mmol/mol)

The US and most patient-facing labs report A1C as a percentage (the NGSP/DCCT scale). The UK, much of Europe, and clinical-chemistry standards use IFCC units (mmol/mol). The master equation that links them:

A1C (mmol/mol) = 10.929 × (A1C% − 2.15)

A1C (%) = A1C(mmol/mol) ÷ 10.929 + 2.15

So a 6.5% A1C is 48 mmol/mol — the UK diagnostic threshold for type 2 diabetes. Per the IFCC reference method (Hoelzel W et al., Clin Chem 2004;50:166–74) and the 2007 international consensus on A1C standardization.

GMI — Glucose Management Indicator (from CGM)

When continuous glucose monitors became common, researchers found that estimating A1C from sensor mean glucose using the old eAG formula was systematically off. GMI is the replacement, derived specifically from CGM data:

GMI (%) = 3.31 + 0.02392 × mean glucose (mg/dL)

GMI and a lab A1C measure the same thing two different ways and often differ by a few tenths of a percent — that difference is clinically meaningful, not an error. Per Bergenstal RM et al., Diabetes Care 2018;41(11):2275–80.

Fructosamine → estimated A1C (approximate)

Fructosamine measures glycated serum proteins, reflecting roughly the prior 2–3 weeks rather than 2–3 months. It's used when A1C is unreliable. The commonly cited regression:

estimated A1C (%) ≈ 0.017 × fructosamine (µmol/L) + 1.61

This conversion is not standardized — multiple published equations exist and the relationship varies by assay and population, so the result is an estimate only. Based on the regression from Cohen RM et al. on the HbA1c–fructosamine relationship; see also the Medscape fructosamine reference.

Worked examples

"My A1C is 7.0% — what's my average blood sugar?"

Enter 7.0 in the A1C field. The tool returns an estimated average glucose of 154 mg/dL (8.6 mmol/L) and an IFCC value of 53 mmol/mol, and classifies it in the diabetes range — but notes that 7% is the under-7 level many adults with diabetes aim for, a target your clinician individualizes. If you check your meter throughout the day, your readings should average roughly 154 mg/dL if the lab A1C is accurate.

"My CGM says my average glucose is 154 — why doesn't my A1C match?"

Enter 154 in the GMI panel and you get a GMI of 7.0%. If your lab A1C came back at 7.4%, the tool flags a 0.4% glucose gap — your A1C runs higher than your CGM-derived estimate. Gaps like this are common and have real causes (red-blood-cell turnover, sensor calibration, the months each marker covers). It's exactly the kind of discrepancy worth raising with your care team rather than dismissing. A home glucose meter can be used to spot-check the sensor against a fingerstick.

"I'm pregnant and my doctor ordered a fructosamine instead of A1C"

In pregnancy, red-cell turnover speeds up and A1C reads falsely low, so fructosamine is sometimes used. Enter a fructosamine of 285 µmol/L and the tool estimates an A1C of about 6.5% — clearly labeled approximate. Because the fructosamine-to-A1C relationship isn't standardized, treat this as a ballpark to discuss with your clinician, not a diagnostic number.

A1C conversion chart

The full A1C ↔ eAG ↔ IFCC reference, per the ADAG study and the NGSP/IFCC master equation:

• A1C 5.0% — eAG 97 mg/dL (5.4 mmol/L) · 31 mmol/mol · Normal
• A1C 5.7% — eAG 117 mg/dL (6.5 mmol/L) · 39 mmol/mol · Prediabetes begins
• A1C 6.0% — eAG 126 mg/dL (7.0 mmol/L) · 42 mmol/mol · Prediabetes
• A1C 6.5% — eAG 140 mg/dL (7.8 mmol/L) · 48 mmol/mol · Diabetes threshold
• A1C 7.0% — eAG 154 mg/dL (8.6 mmol/L) · 53 mmol/mol · Common adult target ceiling
• A1C 8.0% — eAG 183 mg/dL (10.2 mmol/L) · 64 mmol/mol
• A1C 9.0% — eAG 212 mg/dL (11.8 mmol/L) · 75 mmol/mol
• A1C 10.0% — eAG 240 mg/dL (13.4 mmol/L) · 86 mmol/mol
• A1C 11.0% — eAG 269 mg/dL (14.9 mmol/L) · 97 mmol/mol
• A1C 12.0% — eAG 298 mg/dL (16.5 mmol/L) · 108 mmol/mol

Frequently asked questions

What is my A1C if my average blood sugar is 123 mg/dL?

Using the ADAG formula, A1C = (123 + 46.7) ÷ 28.7 = about 5.9%, which falls in the prediabetes range (5.7–6.4%). Enter 123 in the eAG (mg/dL) field above to see it convert live, along with the mmol/L and IFCC equivalents.

How do I convert mg/dL to A1C?

Take your average glucose in mg/dL, add 46.7, and divide by 28.7. For example, an average glucose of 154 mg/dL gives an A1C of 7.0%. The calculator does this instantly — type your number into the eAG (mg/dL) field and read the A1C field.

Is GMI the same as A1C?

No. A1C is a lab measurement of glycated hemoglobin over about three months. GMI (Glucose Management Indicator) is an A1C estimate calculated from the average glucose your continuous glucose monitor records. They usually land within a few tenths of a percent of each other, but a larger gap is meaningful — it can reflect differences in red-blood-cell lifespan, the time windows each covers, or sensor accuracy. Both are useful; they answer slightly different questions.

What A1C is diabetes?

Per the American Diabetes Association, an A1C of 6.5% or higher (48 mmol/mol) on two tests is diagnostic for diabetes; 5.7–6.4% (39–47 mmol/mol) is prediabetes; below 5.7% is normal. This tool classifies your number against those bands, but diagnosis is a clinical decision your doctor makes — not something to conclude from a single converted value.

Can I embed this A1C calculator on my own site?

Yes — copy the snippet at the bottom of this page. The embedded version is a clean, chrome-free widget for diabetes educators, primary-care practices, nursing schools, and patient-education blogs. Attribution is built in. There's no fee, no signup, and no analytics attached to the embed.

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• Browse all free tools by Dr. Taylor →

Dr. Taylor's recommendations alongside this calculator

Converting the number is step one; acting on it is what matters. Three categories cover most of what's worth having when you're tracking A1C — each links to the full review with current top picks, prices, and pros and cons:

• Best Glucose Monitors — your A1C is a three-month average, but a home meter shows the daily pattern behind it. The picks here are graded on ISO 15197 accuracy, strip cost, and connectivity. If your CGM-derived GMI and lab A1C disagree, a fingerstick meter is how you spot-check.
• Best Diabetic Socks — sustained high glucose raises the risk of peripheral neuropathy and foot ulcers. Non-binding, seamless, moisture-wicking socks are inexpensive first-line foot protection for anyone in the diabetes range.
• Best Fiber Supplements — soluble fiber blunts post-meal glucose excursions and is one of the gentlest, best-evidenced first levers. Useful across the prediabetes and diabetes range.

Sources & methodology

• Nathan DM, Kuenen J, Borg R, et al., A1c-Derived Average Glucose Study Group. Translating the A1C assay into estimated average glucose values. Diabetes Care 2008;31(8):1473–8 — the eAG formula.
• Hoelzel W, Weykamp C, Jeppsson JO, et al., IFCC Working Group on HbA1c Standardization. IFCC reference system for measurement of hemoglobin A1c. Clin Chem 2004;50(1):166–74 — the NGSP ↔ IFCC master equation.
• Bergenstal RM, Beck RW, Close KL, et al. Glucose Management Indicator (GMI): A New Term for Estimating A1C From Continuous Glucose Monitoring. Diabetes Care 2018;41(11):2275–80 — the GMI formula.
• Cohen RM, Holmes YR, Chenier TC, Joiner CH. Discordance between HbA1c and fructosamine. — the fructosamine regression (approximate; see also the Medscape fructosamine reference).
• American Diabetes Association. Standards of Care in Diabetes — A1C diagnostic bands (Normal < 5.7%, Prediabetes 5.7–6.4%, Diabetes ≥ 6.5%).

This tool is reviewed annually for citation currency, tracking the ADA's January Standards of Care updates. About Dr. Taylor · Last reviewed June 25, 2026.

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Free for diabetes educators, primary-care practices, endocrinology clinics, nursing schools, and patient-education blogs. Required attribution is included in the snippet. No fee, no signup, no analytics attached to the embed.

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