A1C Calculator
Convert an HbA1c percentage into estimated average glucose in both mg/dL and mmol/L.
Formula and sources updated · Data sources · 1View algorithm, constants and default inputs (JSON)
About this calculator
HbA1c reflects average blood glucose over the previous two to three months, because it measures how much glucose has stuck to haemoglobin — and red blood cells live about that long. The conversion is a straight line fitted to continuous glucose monitoring data, so it is an estimate rather than a measurement.
Worked example
calculated with the default values below
HbA1c 7 % Estimated average glucose 154 mg/dL · Estimated average glucose 8.6 mmol/L · HbA1c 7.0 % Diabetes range
Method and assumptions
eAG in mg/dL = 28.7 × A1C percent - 46.7; the tool converts to mmol/L by dividing by 18.0182. Regression estimate; it does not replace measured glucose or clinical interpretation of A1C.
Data sources
Disclaimer
These calculators are for general information only and are not a medical device, a diagnosis or a treatment plan. Reference ranges describe populations, not individuals, and do not account for pregnancy, medication, disability or athletic training. Discuss your own situation with a qualified healthcare professional.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
eAG = 28.7 × A1C − 46.7
- eAG
- estimated average glucose (mg/dL)
- A1C
- HbA1c value (%)
Divide mg/dL by 18.0182 to obtain mmol/L.
Frequently asked questions
When may an HbA1c result be unreliable?
Conditions that change red-blood-cell lifespan or interfere with the assay can make HbA1c misleading. Examples include recent blood loss or transfusion, some forms of anaemia, kidney disease, and some haemoglobin variants. The calculator only converts an HbA1c value you enter into estimated average glucose; it cannot detect interference. Discuss a result that does not fit your glucose readings with a healthcare professional.
Can this estimate replace a laboratory test?
No. The calculator applies the population equation eAG (mg/dL) = 28.7 × HbA1c − 46.7 to an HbA1c result you provide. It does not measure glucose or HbA1c, and an individual’s measured average glucose may differ from the estimate. Use the output to interpret a laboratory result, not to diagnose or monitor a condition on its own.
Which inputs and limits apply to A1C Calculator?
Use the units shown beside each field. These are form limits, not recommended settings. HbA1c: 3–20 % eAG in mg/dL = 28.7 × A1C percent - 46.7; the tool converts to mmol/L by dividing by 18.0182. Regression estimate; it does not replace measured glucose or clinical interpretation of A1C.
What is a complete worked example for HbA1c = 7 %?
Inputs: HbA1c = 7 %. Calculation: eAG = 28.7 × A1C − 46.7. Results: Estimated average glucose = 154 mg/dL; Estimated average glucose = 8.6 mmol/L; HbA1c = 7.0 %.