A1C to average glucose: the clinical formula behind the eAG number
My doctor mentioned my A1C result and then translated it to an 'estimated average glucose' number that matched my glucometer readings far better than the raw percentage ever could — the formula behind that translation is
We write the way we argue on the bench: exact factor, one sharp trap, one worked example you can re-check.
My doctor mentioned my A1C result and then translated it to an 'estimated average glucose' number that matched my glucometer readings far better than the raw percentage ever could — the formula behind that translation isn't just a simple ratio.
Here is the conversion I wish I had taped to the fridge before that went sideways.
The factor that settles arguments
This is the relationship our converters use. Screenshot it if you have to — just stop re-deriving it from a half-remembered blog post.
eAG (mg/dL) = 28.7 × A1C(%) − 46.7 — an affine formula with both a scale and an offset
Write that line once at the top of your notes. Every later arithmetic step should point back to it instead of inventing a friendlier number mid-stream.
The mistake that keeps showing up
Trying to estimate average glucose from A1C with only a multiplication, skipping the −46.7 offset — since it's an affine formula, dropping the offset systematically overstates the estimated average glucose.
I still write the unit next to every intermediate value. It looks pedantic until it catches the one swap that would have shipped wrong.
- Write down the known value in A1C (%).
- Confirm the target unit is really estimated average glucose (mg/dL), not a similar-looking one.
- Apply the factor: eAG (mg/dL) = 28.7 × A1C(%) − 46.7 — an affine formula with both a scale and an offset.
- Round only at the end, to the precision your tool or spec supports.
Worked example
A lab report shows an A1C of 7.0%, and you want the estimated average glucose (eAG) figure your doctor might reference.
An A1C of 7.0%: eAG = 28.7 × 7.0 − 46.7 = 200.9 − 46.7 = 154.2 mg/dL.
That's an estimated average glucose of about 154 mg/dL — both the multiply and the subtraction matter here, unlike a pure scaling factor.
If you want a second check, invert the conversion and see whether you recover the original quantity within normal rounding.
Quick reference table
| A1C (%) | Calculation | estimated average glucose (mg/dL) |
|---|---|---|
| 6.0% A1C | 28.7×6.0−46.7 | 125.5 mg/dL |
| 7.0% A1C | 28.7×7.0−46.7 | 154.2 mg/dL |
| 8.0% A1C | 28.7×8.0−46.7 | 182.9 mg/dL |
| 9.0% A1C | 28.7×9.0−46.7 | 211.6 mg/dL |
Use the table for speed once you trust the factor. Do not use it as a substitute for understanding which definition of the unit you are on.
Why the exact number matters
Patients and caregivers often compare A1C-derived eAG against daily glucometer readings to sanity-check control — getting the formula wrong misleads that comparison.
Precision is not about showing off decimals. It is about making sure the shopping list, the machine setting, and the acceptance check are all describing the same physical quantity.
Pocket recap
Multiply A1C by 28.7 and subtract 46.7 to get eAG in mg/dL — this is the ADA's published formula, not an approximation you can simplify.
Keep the converter link nearby for the next time the same debate shows up in a group chat. Re-typing the factor from memory is how the wrong cousin of a unit sneaks back in.
Try the converters mentioned in this article
FAQ
What is the exact A1C (%) to estimated average glucose (mg/dL) factor here?+
eAG (mg/dL) = 28.7 × A1C(%) − 46.7 — an affine formula with both a scale and an offset
Should I round partway through the calculation?+
No — carry full precision through the multiplication and round only the final answer, to the precision your tool, gauge, or spec actually supports.
What's the single biggest mistake people make with this conversion?+
Trying to estimate average glucose from A1C with only a multiplication, skipping the −46.7 offset — since it's an affine formula, dropping the offset systematically overstates the estimated average glucose.
This article was written by The Turbo Unit Converter engineering desk (Applied units & field metrology) and last reviewed on 2026-07-18 against NIST SP 811 and the BIPM SI Brochure. Read our full editorial policy.