A1C Calculator

Use this professional-grade calculator to convert between A1C percentage and estimated average glucose (eAG). Built with the clinically validated ADAG formula used by endocrinologists worldwide. All calculations happen in your browser with zero data transmission.

A1C → Estimated Average Glucose

Enter your A1C percentage as shown on your lab results
Choose glucose unit for results
Calculate estimated average glucose from A1C value

Estimated Average Glucose

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mg/dL

Average Glucose → A1C

Enter your average glucose from CGM or meter readings
Choose glucose input unit
Calculate estimated A1C from average glucose

Estimated A1C

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%

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What is A1C?

The A1C test (also called hemoglobin A1C, HbA1c, or glycated hemoglobin test) measures the percentage of your red blood cells that have glucose-attached hemoglobin. This provides a reliable picture of your average blood sugar over the previous 2-3 months.

When glucose circulates in your bloodstream, some naturally attaches to hemoglobin (the oxygen-carrying protein in red blood cells). The higher your blood sugar has been, the more hemoglobin becomes glycated, resulting in a higher A1C percentage.

Medical Standards (ADA 2026)

  • Normal: Below 5.7%
  • Prediabetes: 5.7% to 6.4%
  • Diabetes: 6.5% or higher

How the A1C Conversion Works

This calculator uses the clinically validated ADAG (A1C-Derived Average Glucose) formula established by Nathan et al. in 2008. The study included 507 participants using continuous glucose monitors for precise average glucose measurements.

ADAG Formulas

A1C to Glucose:
eAG (mg/dL) = 28.7 × A1C - 46.7
eAG (mmol/L) = 1.59 × A1C - 2.59
Glucose to A1C:
A1C (%) = (eAG mg/dL + 46.7) / 28.7

Formula Accuracy

  • Correlation coefficient: 0.84 (explains 84% of variance)
  • Standard error: ±15.4 mg/dL
  • Validated across multiple populations and diabetes types

Risk Levels & Medical Interpretation

A1C risk levels with corresponding glucose ranges
A1C Range eAG (mg/dL) eAG (mmol/L) Classification Risk Level
Below 5.7% Below 117 Below 6.5 Normal Low
5.7% to 6.4% 117 to 137 6.5 to 7.6 Prediabetes Moderate
6.5% to 6.9% 140 to 151 7.8 to 8.4 Diabetes (Well Controlled) Elevated
7.0% to 7.9% 154 to 180 8.6 to 10.0 Diabetes (Moderate) High
8.0% and above 183+ 10.2+ Diabetes (Poor Control) Critical

Frequently Asked Questions