HbA1c Calculator

1. Choose what you are entering. Pick HbA1c in percent, HbA1c in mmol/mol, or an average glucose in mg/dL or mmol/L.
2. Type the value. Use the exact figure on the lab report. The tool accepts values that convert to an HbA1c between 3 and 20 percent.
3. Add a target only when you have one. A target from your own clinician shows the gap in A1C points and in mg/dL.

HbA1c is hemoglobin with glucose attached, and the A1C test reports how much of your hemoglobin carries it. The American Diabetes Association describes the test as a measure of average blood glucose for the past two to three months.

Red blood cells live about 120 days, according to the NGSP. The result is a weighted average: glucose levels in the most recent 30 days count more than levels from 90 to 120 days ago.

Labs report the result in one of two units. NGSP units are percent. IFCC units are mmol/mol. The two describe the same blood sample, and a fixed equation links them.

Estimated average glucose, or eAG, restates the A1C in the units of a home glucose meter. The NIDDK notes that eAG will not match single meter readings, because it is a long-term average.

The calculator converts any input to NGSP percent first, then applies three published equations.

1. eAG from A1C. The ADAG study (Nathan and colleagues, Diabetes Care, 2008) compared A1C with about 2,700 glucose readings per person in 507 people. Its regression line is eAG = 28.7 x A1C - 46.7, with R squared 0.84.
2. mg/dL to mmol/L. Glucose has a molar mass of 180.156 g/mol, so 1 mmol/L equals 18.0156 mg/dL.
3. NGSP and IFCC. The NGSP publishes the master equation NGSP = 0.09148 x IFCC + 2.152 and its inverse, IFCC = 10.93 x NGSP - 23.50.
4. Reverse mode. For a glucose input, the tool solves the ADAG line backward: A1C = (eAG + 46.7) / 28.7.

Take an A1C result of 7.0 percent.

1. 28.7 x 7.0 = 200.9.
2. 200.9 - 46.7 = 154.2 mg/dL, shown as 154.
3. 154.2 / 18.0156 = 8.56 mmol/L, shown as 8.6.
4. 10.93 x 7.0 - 23.50 = 53.01, so the IFCC value is 53 mmol/mol.

These figures match the NGSP conversion table: 7.0 percent, 53 mmol/mol, 154 mg/dL and 8.6 mmol/L.

HbA1c Conversion Chart

Whole-percent rows from 5 to 12 agree with the table the NGSP publishes, with one small exception. The NGSP table divides by 18, so it shows 11.8 and 13.4 mmol/L at 9 and 10 percent. This page divides by 18.0156 and shows 11.7 and 13.3.

The conversion is exact arithmetic, but the A1C number itself depends on your blood and on the lab.

Conditions That Change Red Blood Cells

The NIDDK lists anemia, kidney failure, liver disease and transfusion among the causes of a falsely high or low A1C.

Hemoglobin Variants

People of African, Mediterranean or Southeast Asian descent, and people with sickle cell trait or thalassemia in the family, are more likely to carry a variant that interferes with some A1C tests.

Recent Glucose Changes

The last 30 days weigh more than earlier weeks. A large recent change moves the A1C sooner than the 120-day cell lifespan suggests.

Person-to-Person Scatter

The ADAG line explains 84 percent of the variation between A1C and average glucose. Two people with the same A1C can have different true averages.

Rounding

Each 0.1 point of A1C equals 2.87 mg/dL of eAG. Each full point equals 28.7 mg/dL, or about 1.6 mmol/L.

The American Diabetes Association states three A1C ranges for diagnosis.

The percent column is the ADA wording. The other two columns are this page's conversions of those limits. The ADA adds that a test usually needs to be repeated on a second day to diagnose diabetes.

ADAG vs the Older DCCT Equation

An earlier equation from DCCT data was average glucose = 35.6 x A1C - 77.3. At 7.0 percent it gives 171.9 mg/dL, which is 17.7 mg/dL above the ADAG value. The NGSP explains that ADAG used far more glucose readings per person. This tool uses ADAG.

NGSP Percent vs IFCC Mmol/mol

IFCC numbers look very different from NGSP numbers by design, so nobody confuses the two. An IFCC value of 48 mmol/mol converts to 6.54 percent, which labs report as 6.5.

Reading a Lab Report in Other Units

A report in mmol/mol converts to the percent figure used in US guidance, and back.

Relating A1C to Meter Readings

eAG puts the lab result in the units your meter or sensor shows. More background is in our guide to what your A1C number means.

Estimating A1C from a Sensor Average

A long-term average glucose of 154 mg/dL lines up with an A1C near 7.0 percent. It is an estimate only.

Seeing the Size of a Gap

An A1C of 8.2 percent against a clinician target of 7.0 is 1.2 points, or about 34 mg/dL of average glucose.

Study and Teaching

The A1C is a weighted average, the same idea the weighted average calculator works through. The mmol step rests on molar mass, covered by the moles calculator.

1. Treating EAG as a Meter Reading

eAG is a multi-week average. A single reading before breakfast or after a meal will differ from it.

2. Mixing Percent and Mmol/mol

Typing 53 as a percent, or 7 as mmol/mol, gives an error. Check the unit on the report.

3. Diagnosing Yourself

The range label repeats the ADA table. A diagnosis needs a clinician, and usually a second test on another day.

4. Using Fasting Glucose as the Average

The NGSP warns that fasting glucose is a poor stand-in for average glucose, and underestimates it more as A1C rises.

5. Ignoring Test Interference

Anemia or a hemoglobin variant can make the A1C itself misleading. No conversion fixes that.

6. Using the Old DCCT Line

Older charts based on 35.6 x A1C - 77.3 show higher glucose values than the ADAG chart for the same A1C.

The arithmetic follows the published equations exactly and reproduces the percent, mmol/mol and mg/dL columns of the NGSP conversion table. The limits lie in what an A1C can tell one person.

This is not a diagnosis. See a clinician about any result in or near the prediabetes or diabetes range.

The American Diabetes Association lists an A1C below 5.7 percent as normal. That equals less than 39 mmol/mol and an estimated average glucose under 117 mg/dL.

The ADA lists 6.5 percent or higher, which is 48 mmol/mol. A diagnosis is made by a clinician and usually needs a repeat test on a second day.

Multiply the percent by 10.93 and subtract 23.50. For 6.5 percent: 10.93 x 6.5 - 23.50 = 47.5, reported as 48 mmol/mol.

About 126 mg/dL, or 7.0 mmol/L. The equation is 28.7 x 6 - 46.7 = 125.5.

You can estimate it with A1C = (average mg/dL + 46.7) / 28.7. An average of 200 mg/dL gives about 8.6 percent. Only a lab test gives the real value.

eAG is a long-term average, and a meter shows one moment. The NIDDK states that eAG will not match daily readings for that reason.

No. Anemia, kidney or liver disease, transfusion and some hemoglobin variants make results falsely high or low. Your doctor can choose a different test.

They are two unit systems for the same test. NGSP reports percent and IFCC reports mmol/mol. The master equation NGSP = 0.09148 x IFCC + 2.152 links them.

Pregnant women and anyone with anemia, a hemoglobin variant or another blood condition should not rely on it. Those cases need a clinician to pick and read the right test.

No. The math runs in your browser. The Save button keeps results only in your own browser storage.

• IFCC and NGSP master equation and conversion table (NGSP, IFCC Standardization of HbA1c).
• HbA1c and estimated average glucose (eAG) (NGSP).
• Translating the A1C assay into estimated average glucose values (Nathan DM and others, ADAG Study Group, Diabetes Care, 2008; PubMed record).
• Diabetes diagnosis: A1C ranges (American Diabetes Association).
• The A1C test and diabetes (National Institute of Diabetes and Digestive and Kidney Diseases).