Skip to main content
health

A1C Calculator (Hemoglobin A1c)

Convert A1C percentage to estimated average glucose (eAG) in mg/dL and mmol/L. A1C reflects average blood sugar control over 2-3 months.

Reviewed by Chase FloiedUpdated

This free online a1c calculator (hemoglobin a1c) provides instant results with no signup required. All calculations run directly in your browser — your data is never sent to a server. Enter your values below and see results update in real time as you type. Perfect for everyday calculations, homework, or professional use.

How to Use This Calculator

1

Enter your input values

Fill in all required input fields for the A1C Calculator (Hemoglobin A1c). Most fields include unit selectors so you can work in your preferred unit system — metric or imperial, whichever matches your problem.

2

Review your inputs

Double-check that all values are correct and that you have selected the right units for each field. Incorrect units are the most common source of calculation errors and can produce results that are off by factors of 2, 10, or more.

3

Read the results

The A1C Calculator (Hemoglobin A1c) instantly computes the output and displays results with units clearly labeled. All calculations happen in your browser — no loading time and no data sent to a server.

4

Explore parameter sensitivity

Try adjusting individual input values to see how the output changes. This is a quick and effective way to develop intuition about how different parameters influence the result and to identify which inputs have the largest effect.

Formula Reference

A1C Calculator (Hemoglobin A1c) Formula

See calculator inputs for the governing equation

Variables: All variables and their units are labeled in the calculator interface above. Input fields accept values in multiple unit systems — select your preferred unit from the dropdown next to each field.

When to Use This Calculator

  • •Use the A1C Calculator (Hemoglobin A1c) for personal health tracking and wellness monitoring, establishing a baseline and tracking changes over time.
  • •Use it when recording fitness metrics to track progress toward health or athletic goals.
  • •Use it to compare measurements before and after a lifestyle, diet, or training change to quantify the impact.
  • •Use it as a conversation starter before a doctor's appointment, bringing objective data to discuss with a healthcare professional.

About This Calculator

The A1C Calculator (Hemoglobin A1c) is a free health and wellness calculation tool designed for personal use and general informational purposes. Convert A1C percentage to estimated average glucose (eAG) in mg/dL and mmol/L. A1C reflects average blood sugar control over 2-3 months. This calculator provides reference values based on established health screening formulas and should not be used as a substitute for professional medical advice, diagnosis, or treatment. Results may vary based on individual factors not captured by the calculation. Consult a qualified healthcare provider for personalized health guidance. All calculations are performed locally in your browser — no personal health data is transmitted or stored.

About A1C Calculator (Hemoglobin A1c)

The A1C Calculator converts hemoglobin A1c percentages to estimated average glucose (eAG) using the formula established by the ADAG study. A1C reflects your average blood sugar over the previous 2-3 months by measuring the percentage of hemoglobin proteins with glucose attached. It is the primary metric for diagnosing diabetes, monitoring blood sugar control, and guiding treatment. The American Diabetes Association recommends A1C below 7% for most adults with diabetes.

The Math Behind It

Hemoglobin A1c forms when glucose binds to hemoglobin in red blood cells. Because red blood cells live ~120 days, A1C reflects 2-3 month average glucose with more recent weeks weighted more heavily. **A1C classification**: - Normal: <5.7% - Prediabetes: 5.7-6.4% - Diabetes: ≥6.5% - ADA target: <7.0% The ADAG study (2008) established eAG = 28.7 × A1C - 46.7 by comparing A1C with continuous glucose monitoring in 507 participants. R² = 0.84. **Limitations**: Conditions affecting red blood cell lifespan alter A1C accuracy (anemia, transfusions, sickle cell). Fructosamine or glycated albumin may be used as alternatives in these cases.

Formula Reference

ADAG Formula (2008)

eAG (mg/dL) = 28.7 × A1C - 46.7

Variables: A1C = hemoglobin A1c percentage

Worked Examples

Example 1: A1C 7.0%

Diabetic patient with A1C of 7.0%

Step 1:eAG = 28.7 × 7.0 - 46.7
Step 2:= 200.9 - 46.7 = 154.2 mg/dL
Step 3:mmol/L: 154.2 / 18.018 = 8.6

eAG is 154 mg/dL (8.6 mmol/L).

Example 2: Normal A1C 5.5%

Healthy adult with A1C of 5.5%

Step 1:eAG = 28.7 × 5.5 - 46.7 = 111.2 mg/dL
Step 2:mmol/L: 6.2

eAG is 111 mg/dL (6.2 mmol/L) — normal range.

Common Mistakes & Tips

  • !Thinking A1C reflects a single day's blood sugar. It's a 2-3 month weighted average.
  • !Not considering conditions affecting red blood cell turnover.
  • !Using A1C alone to evaluate blood sugar control. A1C doesn't capture glucose variability.

Related Concepts

Blood Sugar Converter

Convert between mg/dL and mmol/L.

Used in These Calculators

Calculators that build on or apply the concepts from this page:

Blood Sugar Converter

GFR Calculator (Kidney Function)

Insulin Dosage Calculator

Frequently Asked Questions

What A1C means diabetes?

6.5% or higher on two tests indicates diabetes. 5.7-6.4% is prediabetes. Below 5.7% is normal.

How often should A1C be tested?

At least twice per year if meeting goals, quarterly if therapy has changed or not meeting targets.