A1C calculator

How do I convert A1C to average blood sugar?

Use the ADAG study formula: estimated average glucose (mg/dL) = 28.7 × A1C − 46.7. An A1C of 7% is about 154 mg/dL, or 8.6 mmol/L.

What do A1C results mean?

Below 5.7% is normal, 5.7% to 6.4% is prediabetes, and 6.5% or higher indicates diabetes (American Diabetes Association and CDC).

What A1C should people with diabetes aim for?

The American Diabetes Association suggests 7% or less for most adults with diabetes; your doctor may set a different goal.

How accurate is estimated average glucose?

It comes from a formula fit across many people, not from your own readings. In the ADAG study, the typical error was about 16 mg/dL (one standard deviation).

Can I estimate A1C from my average glucose?

Yes — choose "A1C from glucose". An average of 154 mg/dL corresponds to an A1C of about 7%.

Where does the formula come from, and how far can I trust it?

The equation comes from the A1C-Derived Average Glucose (ADAG) study (Nathan and colleagues, Diabetes Care, 2008). It analyzed 507 people with type 1 diabetes, type 2 diabetes or no diabetes, each of whom had about 2,700 glucose measurements over three months from continuous monitoring and fingersticks. A straight-line fit of A1C against the average glucose gave eAG (mg/dL) = 28.7 × A1C − 46.7, with R² = 0.84; the same fit in mmol/L is 1.59 × A1C − 2.59. The line describes a group better than any one person: at an A1C of 7% the ADAG table gives 154 mg/dL with a range of 123 to 185 mg/dL, and the standard deviation of the prediction error was 15.7 mg/dL.

Worked example: from an A1C of 8% to average glucose, and back

Multiply the A1C by 28.7: 8 × 28.7 = 229.6. Subtract 46.7: 183 mg/dL, which is 10.2 mmol/L (the ADAG table lists 183 mg/dL for an A1C of 8%). To go the other way, add 46.7 to the glucose and divide by 28.7: an average of 200 mg/dL gives (200 + 46.7) ÷ 28.7 = 8.6%.

What can make an A1C result misleading?

A1C measures the share of hemoglobin in red blood cells that has glucose attached, so anything that changes red blood cells can move the number. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) lists hemoglobin variants, which are more common in people of African, Mediterranean or Southeast Asian descent and can interfere with some A1C tests; conditions such as sickle cell disease that change how long red cells live; iron-deficiency anemia, which can give a falsely high result; kidney failure; and recent blood loss or transfusion. And recent weeks count for more than older ones: glucose from the past 30 days has a greater effect on the result than earlier months.

Common mistakes when reading A1C and average glucose

First, the two scales do not line up with the glucose cutoffs. The diabetes cutoff of 6.5% corresponds to an average glucose of about 140 mg/dL, not 126 mg/dL; 126 mg/dL is the separate fasting plasma glucose cutoff (NIDDK). Second, eAG is not a meter reading. It is a three-month average weighted toward the latest weeks, while a fingerstick is one moment, often fasting, so the two rarely match. Third, the diagnostic ranges are not treatment goals: they apply to people who are not pregnant, a single abnormal result is usually confirmed with a second test, and the ADA goal for many nonpregnant adults with diabetes, below 7% (53 mmol/mol), is individualized by the care team.

Sources and related calculators

Sources: D. M. Nathan et al., “Translating the A1C assay into estimated average glucose values,” Diabetes Care 31 (2008), the ADAG study; NIDDK, “The A1C Test & Diabetes” and its diabetes tests and diagnosis page (diagnostic table); American Diabetes Association, Standards of Care in Diabetes—2026, section 6, “Glycemic Goals, Hypoglycemia, and Hyperglycemic Crises.” Related: BMI calculator, calorie calculator and blood pressure calculator.

For general information only — not medical advice. Talk with your doctor or another health professional about your own health. How we check our calculators.