A1C to Blood Sugar Calculator
Convert A1C percentage to estimated average glucose (eAG) in mg/dL and mmol/L.
See how your A1C compares to normal, prediabetes, and diabetes ranges.
A1C (also called HbA1c or glycated hemoglobin) is a blood test that reflects your average blood sugar level over the past 2-3 months. It works by measuring the percentage of hemoglobin proteins in your red blood cells that have glucose attached to them.
The conversion formula (developed by the ADAG study):
eAG (mg/dL) = (28.7 × A1C) - 46.7
eAG (mmol/L) = eAG (mg/dL) / 18.0
What the variables mean:
- A1C (%) is the percentage from your lab test result, sometimes labelled HbA1c or the DCCT unit
- eAG is estimated Average Glucose, the daily blood sugar level your A1C corresponds to
- mg/dL means milligrams per deciliter, the unit used in the US, Japan, and several other countries
- mmol/L means millimoles per liter, the unit used in the UK, Canada, Australia, and most of Europe
The other A1C unit, and why your lab report may not show a percentage
Outside the US, most labs no longer report A1C as a percentage at all. They use the IFCC unit (International Federation of Clinical Chemistry), written as mmol/mol, which counts millimoles of glycated hemoglobin per mole of total hemoglobin. The UK switched in 2011, and much of Europe followed.
IFCC (mmol/mol) = (A1C% − 2.15) × 10.929
So the familiar 7.0% target is 53 mmol/mol, and 6.5% is 48. The numbers look alarming the first time you see them because the scale is roughly ten times larger, but nothing about the measurement changed. This calculator shows both.
A1C interpretation ranges (per ADA guidelines):
| A1C Level | IFCC | Category | Estimated Avg Glucose |
|---|---|---|---|
| Below 5.7% | Below 39 mmol/mol | Normal | Below 117 mg/dL (6.5 mmol/L) |
| 5.7% - 6.4% | 39-46 mmol/mol | Prediabetes | 117-137 mg/dL (6.5-7.6 mmol/L) |
| 6.5% or higher | 48+ mmol/mol | Diabetes | 140+ mg/dL (7.8+ mmol/L) |
Practical example: An A1C of 7.0% converts to eAG = (28.7 × 7.0) - 46.7 = 154 mg/dL (8.6 mmol/L). This is a common target for adults managing diabetes.
Where the conversion stops being reliable
The eAG formula comes from the ADAG study (A1C-Derived Average Glucose), which enrolled participants across roughly the 5% to 12% range. Below about 5%, the arithmetic still produces a number, but it is an extrapolation rather than a measured relationship, and an A1C of 4.0% would return an eAG of 68 mg/dL that almost nobody actually lives at.
The bigger caveat is scatter. Even inside the validated range, two people with an identical 7.0% can genuinely average 20 to 30 mg/dL apart, because red blood cell lifespan varies. A shorter cell lifespan means less time for glucose to attach, so the A1C reads low for the same true average. That is why continuous glucose monitors report a separate Glucose Management Indicator instead of reusing this formula.
Things that make an A1C misleading: anemia and any condition that shortens red cell survival, recent blood transfusion, pregnancy, chronic kidney disease, and several hemoglobin variants including sickle cell trait. In those situations the percentage is not measuring what it usually measures, and a fructosamine test or a CGM average is the better tool.
Tips: A1C is typically tested every 3-6 months. Always discuss results with your healthcare provider, as individual targets vary with age, health history, and how much hypoglycemia risk a tight target would create.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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