A1C Calculator
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Use this A1C calculator to convert HbA1c reported as NGSP percent or IFCC mmol/mol into estimated average glucose (eAG), or work backward from eAG entered in mg/dL or mmol/L. It uses the published NGSP/ADAG relationships and keeps the health values in your browser tab. The output is for education and record review only, not diagnosis, medication dosing, or urgent treatment decisions.
How the A1C conversion works
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1
Choose a direction and units
Enter laboratory HbA1c as NGSP % or IFCC mmol/mol, or enter eAG as mg/dL or mmol/L.
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2
Apply published relationships
The calculator uses the NGSP/ADAG eAG equation and the NGSP–IFCC master equation, with localized decimal input.
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3
Review the estimate carefully
Only a directly entered A1C receives adult laboratory reference context. An A1C estimated backward from eAG is never treated as a laboratory diagnosis.
A1C and eAG formulas
HbA1c reflects the percentage of hemoglobin that has glucose attached to it over roughly the previous two to three months. Estimated average glucose (eAG) expresses that long-term A1C result in the same glucose units many meters and lab reports use. The relationship is an estimate, so two people with the same A1C can still have different daily glucose patterns.
| Conversion | Formula | Example |
|---|---|---|
| A1C to eAG (mg/dL) | eAG = 28.7 × A1C - 46.7 | 7.0% -> 154 mg/dL |
| eAG to A1C | A1C = (eAG + 46.7) / 28.7 | 154 mg/dL -> 7.0% |
| mg/dL to mmol/L | mmol/L = mg/dL / 18.0182 | 154 mg/dL -> 8.5 mmol/L |
| NGSP % to IFCC mmol/mol | IFCC = (NGSP - 2.152) / 0.09148 | 7.0% -> 53 mmol/mol |
| IFCC mmol/mol to NGSP % | NGSP = 0.09148 × IFCC + 2.152 | 53 mmol/mol -> 7.0% |
Worked example
If an A1C result is 7.0%, multiply 7.0 by 28.7 to get 200.9, then subtract 46.7. The estimated average glucose is 154.2 mg/dL, which rounds to 154 mg/dL. Dividing by 18.0182 gives about 8.6 mmol/L.
Going the other direction, an eAG of 126 mg/dL becomes (126 + 46.7) / 28.7 = 6.02%, so the calculator reports about 6.02% A1C.
Reading the reference bands
The bands shown after a directly entered A1C are informational adult laboratory references only. Many public health references list A1C below 5.7%, 5.7% to 6.4%, and 6.5% or higher, but diagnosis generally requires appropriate certified laboratory testing, clinical interpretation, and confirmation. The calculator does not assign a diagnostic band to an A1C estimated backward from eAG. Lab method, anemia, pregnancy, kidney disease, recent blood loss, transfusion, and hemoglobin variants can all make A1C less representative of actual glucose exposure. A laboratory A1C below 4% or above 15% may also warrant investigation for interference or another issue.
Use this converter to understand units, prepare questions, or compare reports that use different formats. For diagnosis, treatment targets, medication changes, or symptoms of high or low blood sugar, use professional medical advice rather than a web calculator.
Frequently Asked Questions
No. It only converts between HbA1c and estimated average glucose using published formulas. Diagnosis requires appropriate lab testing and clinical interpretation by a qualified healthcare professional.
Not exactly. eAG is estimated from A1C, while a meter or CGM average comes from actual glucose readings over a specific period. They can differ because A1C is affected by red blood cell lifespan and other health factors.
They describe different measurements. mmol/L is a glucose concentration used for eAG, while IFCC mmol/mol is an HbA1c reporting unit. The calculator labels both explicitly and also shows the corresponding mg/dL and NGSP percentage.
No. The conversion runs in the page with your typed numbers. Do not enter private medical identifiers, and use your clinician or lab portal for personal medical record decisions.
No. This tool is educational and should not be used for dosing, urgent care, or treatment changes. Follow your care plan and ask a qualified clinician about medical decisions.
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