Tool
A1c calculator
Type into any field. The others follow: A1c in %, estimated average glucose in mg/dL or mmol/L, and A1c in IFCC units (mmol/mol), which labs in the UK and much of Europe report.
Estimated average glucose (eAG) = 28.7 × A1c − 46.7, from the ADAG study. mmol/L = mg/dL ÷ 18.016. Real averages vary from person to person at the same A1c. This is a conversion, not a diagnosis.
The formulas
A1c to average glucose. The A1c-Derived Average Glucose (ADAG) study compared A1c with glucose measured many times a day over about three months, and found a straight-line relationship (Nathan 2008). The ADA uses it in its own eAG calculator (ADA eAG).
A1c (%) = (eAG + 46.7) ÷ 28.7
mg/dL and mmol/L. Glucose in mmol/L is mg/dL divided by 18.016, the conversion that follows from glucose's molecular weight.
% and mmol/mol. The NGSP master equation links the two A1c scales (NGSP).
How to read the result
- eAG is a long-term average. It will not match a single meter reading, which is one moment in time (NIDDK).
- The relationship is an average across people. Two people with the same A1c can have different true average glucose. The ADAG paper reports this spread (Nathan 2008).
- The category shown (normal, prediabetes, diabetes) uses the ADA cut points of 5.7% and 6.5% (ADA Standards 2026, sec. 2). A diagnosis needs a lab test and, without symptoms, a confirming second test (NIDDK).
- Some conditions make A1c less accurate. See when A1c can mislead.
- Using a home kit? See how accurate home A1c tests are.
Your lab reports mmol/mol? Use the mmol/mol converter and chart, with UK ranges. Want every value in one place? See the A1c chart. Using a CGM? Try the GMI calculator. Calculadora de A1c en español.
Sources
- Nathan DM, Kuenen J, Borg R, Zheng H, Schoenfeld D, Heine RJ; A1c-Derived Average Glucose (ADAG) Study Group. Translating the A1C assay into estimated average glucose values. Diabetes Care. 2008;31(8):1473-1478. doi.org/10.2337/dc08-0545
- American Diabetes Association. eAG/A1C conversion calculator (professional.diabetes.org). professional.diabetes.org/glucose_calc
- NGSP. IFCC Standardization of HbA1c: the IFCC and NGSP master equation (NGSP = 0.09148 x IFCC + 2.152). ngsp.org/ifccngsp.asp
- American Diabetes Association Professional Practice Committee. 2. Diagnosis and Classification of Diabetes: Standards of Care in Diabetes 2026. Diabetes Care. 2026;49(Suppl 1). doi.org/10.2337/dc26-S002
- National Institute of Diabetes and Digestive and Kidney Diseases (NIH). The A1C Test & Diabetes. www.niddk.nih.gov/health-information/diagnostic-tests/a1c-test
Written and maintained by the controla1clevels.com editorial team. We do not have a medical reviewer; every claim links to its primary source above. Last reviewed: 2026-10-25. Spotted an error? See About.