Online Tool Store
· 4 min read
How to Convert A1C to Average Blood Glucose
Heshan Fernando
Co-founder & COO
Your lab results come back with “A1C: 6.8%” and a note from your clinic that doesn’t explain what that percentage actually means in the numbers your glucose meter shows every day. You check your fasting glucose most mornings in mg/dL (or mmol/L, depending where you live), so a lab value with no obvious relationship to those daily numbers is hard to make sense of on its own.
This gap comes up constantly for anyone managing diabetes or prediabetes alongside a home glucose meter or continuous glucose monitor. The A1C test measures something different — average blood sugar over roughly the past two to three months, based on how much glucose has attached to hemoglobin in your red blood cells — and translating that percentage into a daily-average glucose figure takes a specific, published formula, not guesswork.
What A1C to average glucose conversion actually involves
The A1C-to-eAG (estimated average glucose) relationship comes from the ADAG (A1C-Derived Average Glucose) study, which correlated A1C percentages with actual average glucose readings from continuous monitoring across a large study population. The commonly used formula is:
eAG (mg/dL) = 28.7 × A1C − 46.7
From there, converting mg/dL to mmol/L is a straightforward unit conversion (divide by 18), giving you the same estimate in whichever unit your region and glucose meter use.
The key word is estimated. This formula gives a population-level average relationship, not a personal guarantee — two people with the same A1C can have somewhat different actual average glucose due to individual variation in red blood cell lifespan and other factors.
Why people get stuck here
- A1C and daily glucose readings use completely different scales. A percentage and a mg/dL or mmol/L reading have no visually obvious relationship, so mental math doesn’t work.
- mg/dL and mmol/L aren’t interchangeable without conversion. The US commonly uses mg/dL; much of the rest of the world uses mmol/L, so even the eAG number needs a second conversion step depending on your meter.
- The formula isn’t something most people memorize. Doctors and educators reference it, but patients rarely get handed the actual equation to check the math themselves.
- A1C reflects an average, not a snapshot. People sometimes expect it to match their most recent glucose reading, when it actually reflects roughly the last 2-3 months blended together.
What a good A1C converter should do
Use the published ADAG formula, not a rough approximation
Because this number can inform real health decisions, a converter should be transparent about using the actual ADAG-derived formula rather than a simplified guess, and ideally show which formula it’s using.
Support both mg/dL and mmol/L output
Since glucose meters and regional norms split between these two units, a converter limited to only one forces an extra manual step for half its users.
Be clearly framed as an estimate, not a diagnosis
The output is useful for context and tracking trends over time, but it isn’t a substitute for discussing lab results with a clinician, especially near diagnostic thresholds.
Common mistakes to avoid
- Treating the eAG estimate as an exact daily glucose target rather than a rough average over months.
- Comparing an eAG figure in mg/dL directly against a meter reading in mmol/L without converting.
- Assuming a single A1C test reflects a recent spike or dip in glucose — it smooths out short-term variation by design.
- Using an A1C-to-glucose conversion in place of medical advice when a reading is near a diagnostic threshold.
- Forgetting that certain conditions (anemia, some hemoglobin variants) can skew A1C results independent of actual average glucose, which a plain conversion formula can’t account for.
How to do it with A1C to Average Glucose Converter
Online Tool Store’s A1C to Average Glucose Converter runs entirely in your browser using the ADAG study formula.
- Open the A1C to Average Glucose Converter.
- Enter your A1C percentage from your lab result.
- Choose whether you want the estimated average glucose shown in mg/dL or mmol/L.
- Read the converted eAG value instantly, ready to compare against your meter’s typical readings.
Frequently asked questions
Is eAG the same as my daily average glucose meter reading?
Not exactly — eAG estimates an average based on your A1C using a population-derived formula, while your meter shows actual individual readings. They should trend similarly over time, but day-to-day numbers won’t match the eAG figure precisely.
What formula does the A1C to average glucose conversion use?
The commonly used formula is eAG (mg/dL) = 28.7 × A1C − 46.7, derived from the ADAG study that correlated A1C percentages with continuous glucose monitoring data.
Can I use this instead of asking my doctor about my results?
No. This conversion is a helpful way to understand what an A1C percentage roughly translates to in familiar glucose units, but interpreting lab results — especially near diagnostic thresholds — should involve your clinician, who has your full history and other lab context.
Final thought
An A1C percentage becomes a lot more concrete once it’s expressed in the same units your glucose meter already uses. Use the conversion to understand the number, not to replace the conversation with whoever ordered the test.