Blood Glucose to HbA1c Calculator
Estimate HbA1c percentage from an average blood glucose in mg/dL or mmol/L, using the ADAG regression line.
Did this tool work for you?
How to use this calculator
The ADAG study regression (Nathan et al., Diabetes Care 2008) gives eAG (mg/dL) = 28.7 × HbA1c − 46.7; the tool inverts it to turn average plasma glucose in mg/dL into an HbA1c percentage. For mmol/L, first multiply by 18.016 to convert to mg/dL before applying the formula.
- 1
Enter an average glucose value in the box.
- 2
Choose mg/dL or mmol/L from the Unit dropdown.
- 3
Read the estimated HbA1c percentage and the glucose shown in both units.
- 4
Treat the band line as text built into this tool; a diagnosis or target comes from a clinician and a laboratory HbA1c.
Frequently asked questions
What equation does the tool use?
HbA1c (%) = (average glucose in mg/dL + 46.7) ÷ 28.7. It is the rearranged form of the published line average glucose = 28.7 × HbA1c − 46.7. The result is rounded to one decimal place before the band is chosen, so the band always matches the percentage on screen.
Which units does it handle?
Glucose can be typed in mg/dL or mmol/L. mmol/L is multiplied by 18.016 to reach mg/dL, and mg/dL is divided by 18.016 for the mmol/L line, shown to two decimals. HbA1c comes out as a percentage only; there is no mmol/mol output.
Does it convert an HbA1c back into glucose?
No. It runs in one direction, from a glucose value to an estimated HbA1c, despite the description saying “convert between”. To go the other way you would apply average glucose = 28.7 × HbA1c − 46.7 yourself.
Can I enter a single reading?
The tool accepts any positive number, but the equation describes an average over weeks to months. One reading is not that average, so the output for it shows the arithmetic only. Typing 100 mg/dL gives 5.1% and typing 240 mg/dL gives 10.0%.
What do the band lines mean?
They are bands built into this tool, chosen by the rounded percentage: below 5.7, 5.7 to under 6.5, 6.5 to under 8.0, and 8.0 or more. The 5.7 and 6.5 lines match the ADA HbA1c cut-offs used in its diagnostic categories, but those apply to a laboratory HbA1c, not to an estimate from a glucose figure; the 8.0 line is this tool’s own. The bands are not a diagnosis or a target.
Why might a laboratory HbA1c differ?
The tool draws one fixed straight line. A laboratory measures haemoglobin directly, and that value can depend on red-cell lifespan and other factors the tool has no input for. A gap of several tenths of a percentage point between the two is not unusual.
What if the glucose box is empty or zero?
An emptied box counts as 0, and the tool shows the prompt “Enter a glucose value” instead of a percentage. Negative numbers are treated as 0 and get the same prompt. A zero would otherwise have produced about 1.6%.
Is this medical advice?
No. It converts units and estimates a percentage from one fixed equation, and does not replace laboratory results. A clinician decides how any glucose or HbA1c figure is interpreted and what targets apply to you.
Blood glucose to HbA1c calculator — estimating A1c from average glucose
The line behind the number
HbA1c reflects the share of haemoglobin carrying glucose, which follows average blood sugar over the red-cell lifespan. The tool takes a single glucose figure and has no memory of earlier entries, so it cannot show a trend between two visits. Studies that paired continuous glucose data with laboratory results produced a straight line: average glucose in mg/dL equals 28.7 times HbA1c minus 46.7. The tool inverts that line. You supply an average glucose, it adds 46.7, divides by 28.7, and rounds the percentage to one decimal. As a check, 126 plus 46.7 is 172.7, and 172.7 divided by 28.7 is 6.017, which the tool prints as 6.0%.
Unit handling as coded
The unit dropdown switches between mg/dL and mmol/L. For mmol/L the tool multiplies by 18.016 to reach mg/dL before the equation runs, and for mg/dL it divides by 18.016 to show the mmol/L figure. Both glucose lines appear beside the result, to one and two decimals. HbA1c appears only as a percentage; mmol/mol is not produced. The mmol/L line is derived rather than re-entered: 7 mmol/L reports 126.1 mg/dL because 7 × 18.016 is 126.112, and 126 mg/dL reports 6.99 mmol/L after dividing by the same factor.
Six runs of the calculator
Each row was produced by running the tool. The 126 mg/dL and 7 mmol/L rows land on the same percentage because 7 mmol/L is 126.1 mg/dL.
| Entered | mg/dL | mmol/L | HbA1c | Band printed by the tool |
|---|---|---|---|---|
| 100 mg/dL | 100.0 | 5.55 | 5.1% | Below 5.7% |
| 126 mg/dL | 126.0 | 6.99 | 6.0% | 5.7% to 6.4% |
| 7 mmol/L | 126.1 | 7.00 | 6.0% | 5.7% to 6.4% |
| 154 mg/dL | 154.0 | 8.55 | 7.0% | 6.5% to 7.9% |
| 10 mmol/L | 180.2 | 10.00 | 7.9% | 6.5% to 7.9% |
| 240 mg/dL | 240.0 | 13.32 | 10.0% | 8.0% or above |
Zero, negatives and rounding
An emptied box is read as zero, and zero or a negative number returns the prompt “Enter a glucose value” rather than a percentage. The band line compares the percentage after rounding to one decimal, so 116 mg/dL, which computes to about 5.67, shows 5.7% and the 5.7%-to-6.4% band together.
Limits and scope
The line is an average across many people, and this tool has no input for anaemia, pregnancy, kidney disease, haemoglobin variants or recent blood loss. A laboratory HbA1c measured from a blood sample outranks the estimate here. The tool converts units and estimates a percentage. This page is general information, not medical advice and not for clinical decisions; interpretation and targets belong to a clinician who sees the full picture. The band lines are fixed strings in the code and attach to any value typed, whether or not it is a true average.
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Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →