A1C Calculator

What this A1C Calculator does

This English-language A1C calculator converts HbA1c percentage values to estimated average glucose (eAG) — and back — using the Nathan 2008 ADAG equation endorsed by the American Diabetes Association. Most hemoglobin A1C calculators only go one direction; this tool handles both, supports mg/dL (standard in the U.S.) and mmol/L (used in most other countries), and immediately labels your result against ADA diagnostic thresholds so you can see whether the value falls in the normal, prediabetes, or diabetes range. The math runs entirely in your browser — 100% client-side — your data never leaves your browser. No uploads, no tracking, no server logs. Whether you've just returned from a clinic visit and want to translate a lab number into a more tangible daily average, or you're working backward from a CGM-estimated glucose to an expected A1C, this hemoglobin A1C calculator gives you the answer in one step.

Features

• Bidirectional conversion. Switch between A1C → eAG and eAG → A1C modes. Enter either value and get the other — useful whether you're reading a lab report or setting a glucose target.
• mg/dL and mmol/L support. Toggle between U.S. mg/dL and international mmol/L with a single click. Results update immediately, so you can share numbers with providers or family members using different units.
• ADA threshold overlay. Every result is automatically classified as Normal (< 5.7%), Prediabetes (5.7%–6.4%), or Diabetes (≥ 6.5%) using the current ADA Standards of Care criteria — no separate lookup needed.
• ADAG equation accuracy. The NIDDK A1C reference confirms the Nathan 2008 regression (eAG = 28.7 × A1C − 46.7) as the population-level standard. This calculator uses that exact formula, not a rounded approximation.
• YMYL-aware disclaimer. An inline warning flags conditions — sickle-cell trait, thalassemia, CKD with erythropoietin, recent transfusion, pregnancy — where A1C is a poor proxy for average glucose, so you know when to rely on CGM data instead.
• No install, no account. Works in any modern browser on desktop or mobile. Nothing is stored, nothing is sent remotely. The calculation is also a good complement to tools like the [BMI calculator](/en/bmi-calculator/) when tracking overall metabolic health.

How to use the A1C Calculator

Three fields, one result — pick your direction, enter the known value, and read the output.

1. Choose a conversion direction. Select 'A1C → eAG' if you have a lab HbA1c percentage and want the daily glucose equivalent, or 'eAG → A1C' if you're working backward from a CGM average.
2. Set your glucose unit. Pick mg/dL if you're in the U.S. (most meters and lab reports use this), or mmol/L for Canadian, European, or Australian values. The conversion factor is 18.018, so 154 mg/dL ≈ 8.6 mmol/L.
3. Enter the known value. Type your HbA1c percentage (e.g. 6.5) or your average glucose (e.g. 140). Accept one decimal place for A1C; the eAG field rounds to a whole number in mg/dL.
4. Read the result and ADA category. The calculator displays the converted value alongside the ADA threshold label. An A1C of 6.5% maps to roughly 140 mg/dL eAG and falls in the Diabetes category — the kind of quick sanity-check that's easy to miss when staring at a raw lab printout.
5. Check the disclaimer for edge cases. If any of the flagged conditions apply to you (hemoglobin variants, pregnancy, recent transfusion, CKD on EPO), the A1C ↔ eAG relationship may not hold. Your clinician may prefer fructosamine or CGM time-in-range in those situations.

Common use cases

• Post-visit lab translation. You leave your endocrinologist's office with an A1C of 7.2% and want to understand what that means day-to-day. The calculator shows ~160 mg/dL eAG — a concrete number that connects to what your meter readings look like throughout the week.
• CGM cross-check. Continuous glucose monitors report a Glucose Management Indicator (GMI) or estimated A1C derived from sensor data. Comparing that figure against your actual lab A1C using this blood glucose A1C converter quickly reveals whether the two are tracking together or diverging — which can signal a calibration issue or a condition affecting red-cell lifespan.
• Insulin titration planning. When adjusting basal insulin or an oral agent toward a target A1C of 7.0%, working out the corresponding eAG target (~154 mg/dL) gives you and your care team a daily glucose number to aim for between quarterly labs.
• Newly diagnosed patient education. For someone newly diagnosed with Type 1 or Type 2 diabetes, an A1C of 9% can feel abstract. Translating it to ~212 mg/dL average glucose — and seeing it labeled as well above the diabetes threshold — often makes the treatment conversation more concrete. The [TDEE calculator](/en/tdee-calculator/) can complement this when discussing dietary changes alongside glucose management.
• International unit reconciliation. A patient in Seattle who recently moved from Dublin may have European lab reports in mmol/L and a U.S. meter in mg/dL. Toggling the unit on this A1C calculator reconciles both sets of numbers without manual division by 18.

Frequently asked questions