A1C Calculator

Q: What A1C equals 140 average blood sugar?

An estimated average glucose (eAG) of about 140 mg/dL corresponds to an A1C of approximately 6.5%. This conversion is based on the ADAG formula used in diabetes care guidelines to relate long-term A1C values to average blood glucose levels over the past two to three months.

Q: What is an A1C calculator?

An A1C calculator estimates hemoglobin A1C or converts it to estimated average glucose (eAG). It helps interpret long-term blood sugar levels over the past two to three months using clinically accepted conversion formulas, rather than single daily glucose readings.

Q: How does the A1C calculator work?

The A1C calculator uses the ADAG research formula to estimate A1C from average blood sugar. It applies a validated relationship where about 46.7 is added to average glucose (mg/dL) and divided by ~28.7. The reverse formula is often shown as: 28.7 × A1C − 46.7 = estimated average glucose (eAG).

Q: How accurate is an A1C calculator?

An A1C calculator provides a close estimate based on population-validated formulas, but individual results may vary. Factors such as red blood cell lifespan, anemia, pregnancy, or certain medical conditions can affect laboratory A1C results compared with calculated estimates.

Q: What is a normal A1C range?

A normal A1C level is below 5.7%. Values between 5.7% and 6.4% are classified as prediabetes, while an A1C of 6.5% or higher meets the diagnostic threshold commonly used for diabetes in clinical settings.

Q: Can I convert average blood sugar to A1C?

Yes. An A1C calculator can estimate A1C from average blood glucose values measured in mg/dL or mmol/L. This conversion reflects long-term glucose exposure rather than short-term fluctuations from individual finger-stick or continuous glucose readings.

Q: What units does the A1C calculator support?

This A1C calculator supports multiple units, including A1C percentage, estimated average glucose in mg/dL and mmol/L, and IFCC mmol/mol. Supporting multiple units allows consistent interpretation across international lab standards and glucose measurement systems.

Q: Can high blood sugar cause fatigue?

Yes. When blood glucose stays elevated for long periods, the body’s cells cannot efficiently convert sugar into usable energy. This can lead to symptoms such as tiredness, reduced stamina, and difficulty concentrating. Learn more about why diabetes causes fatigue and how to boost energy .

The A1C calculator converts hemoglobin A1C (HbA1c), also known as glycated hemoglobin, into estimated average glucose (eAG) and converts eAG back into A1C using ADA-validated formulas. It helps interpret long-term blood sugar trends over about 2–3 months, supporting diabetes monitoring, education, and general metabolic health awareness.

A1C, eAG, and IFCC Conversion Calculator

Instantly convert A1C to estimated average glucose (eAG) or convert eAG back to A1C, in mg/dL or mmol/L, plus IFCC values using the ADAG formula.

Enter A1C (%) Typical range: 4.0% – 14.0%

Enter eAG (mg/dL) Usual range: 70 – 350 mg/dL

eAG (mmol/L) Auto-calculated from mg/dL ÷ 18

IFCC (mmol/mol) Expected: 20 – 130 mmol/mol

Results: —% A1C · — mg/dL (— mmol/L) · — mmol/mol IFCC

Example: A1C 6.5% is approximately 140 mg/dL (7.8 mmol/L) • IFCC 48 mmol/mol

Reference: Normal < 5.7% · Prediabetes 5.7–6.4% · Diabetes ≥ 6.5%

Conversions use the ADAG relationship.² Results are estimates and may vary.

For educational purposes only. Always consult a qualified healthcare professional for medical decisions.

How to Use the A1C Calculator

Enter your hemoglobin A1C value (%) to convert it into estimated average glucose (eAG).
You can also enter your average blood sugar (eAG) in mg/dL to convert it into A1C.
The calculator instantly converts the values using the ADAG formula, which estimates average blood glucose over the past 2–3 months.

This quick conversion helps people understand the relationship between long-term A1C levels and average daily blood sugar.

How to Interpret Your A1C Calculator Results

This A1C calculator converts A1C and estimated average glucose (eAG) using clinically accepted formulas aligned with standards used in diabetes care.¹ A1C reflects average blood sugar levels over approximately two to three months, rather than day-to-day glucose fluctuations seen with individual readings.³

Use the calculated values above as a general reference.⁴ Laboratory A1C results may vary slightly based on individual physiology, testing methods, and certain medical conditions. To understand what your A1C range typically indicates — including normal, prediabetes, and diabetes thresholds — interpret your A1C results using our detailed explanation guide.

The chart below shows how A1C values are commonly grouped in clinical practice, including normal, prediabetes, and diabetes categories.

A1C Chart (What Your % Typically Means)

This chart shows how A1C percentages generally relate to estimated average glucose (eAG) and commonly used diagnostic categories.

A1C (%)	eAG (mg/dL)	eAG (mmol/L)	Category
Below 5.7%	Below 117	Below 6.5	Normal
5.7 – 6.4%	117 – 137	6.5 – 7.6	Prediabetes
6.5% and higher	140 and higher	7.8 and higher	Diabetes

Reference ranges based on the ADAG study. Individual targets may vary. Always discuss A1C results with a healthcare professional.

FAQs

An estimated average glucose (eAG) of about 140 mg/dL corresponds to an A1C of approximately 6.5%. This conversion is based on the ADAG formula used in diabetes care guidelines to relate long-term A1C values to average blood glucose levels over the past two to three months.

An A1C calculator estimates hemoglobin A1C or converts it to estimated average glucose (eAG). It helps interpret long-term blood sugar levels over the past two to three months using clinically accepted conversion formulas, rather than single daily glucose readings.

The A1C calculator uses the ADAG research formula to estimate A1C from average blood sugar. It applies a validated relationship where about 46.7 is added to average glucose (mg/dL) and divided by ~28.7. The reverse formula is often shown as: 28.7 × A1C − 46.7 = estimated average glucose (eAG).

An A1C calculator provides a close estimate based on population-validated formulas, but individual results may vary. Factors such as red blood cell lifespan, anemia, pregnancy, or certain medical conditions can affect laboratory A1C results compared with calculated estimates.

A normal A1C level is below 5.7%. Values between 5.7% and 6.4% are classified as prediabetes, while an A1C of 6.5% or higher meets the diagnostic threshold commonly used for diabetes in clinical settings.

Yes. An A1C calculator can estimate A1C from average blood glucose values measured in mg/dL or mmol/L. This conversion reflects long-term glucose exposure rather than short-term fluctuations from individual finger-stick or continuous glucose readings.

This A1C calculator supports multiple units, including A1C percentage, estimated average glucose in mg/dL and mmol/L, and IFCC mmol/mol. Supporting multiple units allows consistent interpretation across international lab standards and glucose measurement systems.

Yes. When blood glucose stays elevated for long periods, the body’s cells cannot efficiently convert sugar into usable energy. This can lead to symptoms such as tiredness, reduced stamina, and difficulty concentrating. Learn more about why diabetes causes fatigue and how to boost energy.

Embed Our A1C Calculator on Your Website

Copy Embed Code

<!-- DiabetesKnow A1C Calculator Embed -->
<div class="dk-a1c">
  <label>A1C (%)</label>
  <input type="number" step="0.1" id="a1c" placeholder="6.5"/>

  <label>eAG (mg/dL)</label>
  <input type="number" step="1" id="eag" placeholder="140"/>

  <label>IFCC (mmol/mol)</label>
  <input type="number" step="1" id="ifcc" placeholder="48"/>

  <p class="dk-credit">
    Powered by
    <a href="https://diabetesknow.com/health-tools/a1c-calculator/"
       title="A1C Calculator (A1C ↔ Estimated Average Glucose)" target="_blank" rel="noopener">
      DiabetesKnow A1C Calculator
    </a>
  </p>
</div>

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<script type="pmdelayedscript" data-cfasync="false" data-no-optimize="1" data-no-defer="1" data-no-minify="1">
(function(){
  const a1c=document.getElementById('a1c');
  const eag=document.getElementById('eag');
  const ifcc=document.getElementById('ifcc');
  if(!a1c||!eag||!ifcc) return;

  let lock=false;
  const r=(n,d=1)=>Math.round(n*Math.pow(10,d))/Math.pow(10,d);
  const a1cToEag=a=>28.7*a-46.7;
  const eagToA1c=e=>(e+46.7)/28.7;
  const a1cToIfcc=a=>(a-2.15)*10.929;
  const ifccToA1c=i=>i/10.929+2.15;

  a1c.oninput=()=>{ if(lock) return;
    const v=parseFloat(a1c.value); if(!isFinite(v)) return;
    lock=true;
    eag.value=r(a1cToEag(v),0);
    ifcc.value=r(a1cToIfcc(v),0);
    lock=false;
  };

  eag.oninput=()=>{ if(lock) return;
    const v=parseFloat(eag.value); if(!isFinite(v)) return;
    const a=eagToA1c(v);
    lock=true;
    a1c.value=r(a,1);
    ifcc.value=r(a1cToIfcc(a),0);
    lock=false;
  };

  ifcc.oninput=()=>{ if(lock) return;
    const v=parseFloat(ifcc.value); if(!isFinite(v)) return;
    const a=ifccToA1c(v);
    lock=true;
    a1c.value=r(a,1);
    eag.value=r(a1cToEag(a),0);
    lock=false;
  };
})();
</script>
<!-- /DiabetesKnow Embed -->

Free to embed with attribution. Adjust width or styling if needed.

Cite This A1C Calculator

This A1C Calculator is a free, non-commercial tool designed specifically for editorial reference, patient education, and academic use. It converts A1C ↔ estimated average glucose (eAG) in both mg/dL and mmol/L using the ADA-aligned formula.

No account, ads, or product promotion
Bidirectional A1C ↔ eAG conversion
Patient-friendly interpretation guidance
Suitable for editorial, clinical education, and academic reference

Recommended citation:

DiabetesKnow. “A1C Calculator (A1C ↔ Estimated Average Glucose).” https://diabetesknow.com/health-tools/a1c-calculator/

Embed This A1C Calculator

Calculation based on the ADA-accepted relationship between A1C and estimated average glucose.

New to A1C? Read our complete A1C Explained guide to understand what your results mean.

Clinical References & Methodology

ADA eAG/A1C Conversion (formula reference)
American Diabetes Association (Professional). eAG/A1C Conversion Calculator. View source Back to content ↑
ADAG Study
Nathan DM et al. Translating the A1C assay into estimated average glucose values. Diabetes Care, 2008. PubMed Back to content ↑
NGSP: HbA1c and Estimated Average Glucose
National Glycohemoglobin Standardization Program. View source Back to content ↑
ADA Standards of Care
American Diabetes Association. Glycemic Goals & A1C interpretation. View source Back to content ↑

Reviewed by Dr. Seshadri Das, Endocrinologist
Written by Diabetesknow Research Team
Last updated: February 2026