A1C Calculator

What is an A1C calculator?

An A1C calculator converts between your A1C percentage and your estimated average glucose (eAG) — your average blood sugar over the past 2–3 months, shown in both mg/dL and mmol/L. It turns a lab percentage into the same units your glucose meter uses, so the two are easy to compare.

A1C (also written HbA1c, or glycated haemoglobin) measures the share of your haemoglobin that has glucose attached to it. Because red blood cells live around three months, A1C captures a long-run average rather than a single moment. This tool also works in reverse: enter an average glucose value and it estimates the matching A1C.

How do you convert A1C to average glucose?

The calculator uses the ADAG (A1C-Derived Average Glucose) study formula, the same equation the American Diabetes Association uses:

eAG (mg/dL) = 28.7 × A1C − 46.7

To convert that result to mmol/L, divide by 18.0182. To go from glucose back to A1C, the tool rearranges the equation:

A1C (%) = (eAG + 46.7) ÷ 28.7

So the three numbers are linked: pick any one and the other two follow. The widget rounds eAG (mg/dL) to a whole number, shows mmol/L to one decimal, and labels the range as Normal, Prediabetes or Diabetes based on the A1C.

Worked example 1 — A1C to eAG

Suppose your lab reports an A1C of 6.5%:

• eAG = 28.7 × 6.5 − 46.7 = 186.55 − 46.7 = 139.85 mg/dL, which rounds to 140 mg/dL.
• In mmol/L: 139.85 ÷ 18.0182 = 7.8 mmol/L.
• Because 6.5% is at the diabetes threshold, the range shows Diabetes.

Worked example 2 — glucose back to A1C

Your meter averages 154 mg/dL over a few weeks. Switch the tool to Average glucose mode:

• A1C = (154 + 46.7) ÷ 28.7 = 200.7 ÷ 28.7 = 7.0%.
• eAG in mmol/L: 154 ÷ 18.0182 = 8.5 mmol/L.
• An A1C of 7.0% sits in the Diabetes range, and is also a common treatment target for many adults with diabetes.

What is a normal A1C level?

For most non-pregnant adults, an A1C below 5.7% is considered normal, 5.7%–6.4% is prediabetes, and 6.5% or higher (confirmed on a repeat test) is diabetes. These are the standard diagnostic cut-offs, but personal targets vary — many people with diabetes aim for under 7%, while older adults or those with other conditions may have a higher goal set by their clinician.

Category	A1C range	Typical eAG (mg/dL)	Typical eAG (mmol/L)
Normal	Below 5.7%	Below 117	Below 6.5
Prediabetes	5.7% – 6.4%	117 – 137	6.5 – 7.6
Diabetes	6.5% and above	140 and above	7.8 and above

A1C to eAG conversion chart

This table matches the calculator’s output exactly. Use it as a quick reference, then enter your own number above for a precise result.

A1C	eAG (mg/dL)	eAG (mmol/L)	Range
5.0%	97	5.4	Normal
5.5%	111	6.2	Normal
5.7%	117	6.5	Prediabetes
6.0%	125	7.0	Prediabetes
6.5%	140	7.8	Diabetes
7.0%	154	8.6	Diabetes
8.0%	183	10.2	Diabetes
9.0%	212	11.7	Diabetes

How is A1C different from a single glucose reading?

A finger-stick or meter reading captures one moment, while A1C summarises roughly three months of blood sugar in a single percentage. A reading of 180 mg/dL after lunch might be fine on its own, but a string of high readings is what pushes A1C up.

That difference makes each test useful for a different job:

• Day-to-day glucose readings help you react: spotting how a meal, dose, illness or workout moves your numbers right now.
• A1C helps you and your clinician judge the bigger trend and whether a treatment plan is working over time.

eAG is the bridge between them. By converting your A1C into mg/dL or mmol/L, you can see whether your meter readings line up with your long-term average — or whether one half of the picture is hiding spikes the other is missing.

Real-world uses and tips

People use A1C-to-eAG conversion to:

• Understand a lab result that is reported only as a percentage, by seeing it in familiar glucose units.
• Set and track goals — for example, working to bring an A1C from 8.0% (eAG ≈ 183 mg/dL) down toward 7.0% (eAG ≈ 154 mg/dL).
• Reconcile units when a lab in one country reports A1C and a meter reports mmol/L.

A few tips and common mistakes to avoid:

• Don’t confuse eAG with your meter’s own average. eAG is a population estimate from the formula, not a reading from your device.
• Enter A1C as a percentage, not a decimal — type 6.5, not 0.065.
• One number is not a diagnosis. Diabetes is confirmed with repeat testing, ideally on a separate day.
• Big lifestyle changes take time to show. Because A1C reflects ~3 months, a new routine may not move it for several weeks.

For other quick health and math conversions, see more tools in the health & medical category, or try the BMI calculator and the chronological age calculator.

Limitations and accuracy notes

The 28.7 / 46.7 equation is a statistical average from the ADAG study, so it fits most adults well but not everyone. Your real average glucose can sit above or below the eAG estimate, and conditions that change red-blood-cell turnover — anaemia, recent blood loss or transfusion, pregnancy, certain haemoglobin variants, and some kidney or liver conditions — can make A1C itself less reliable. In those cases a clinician may rely more on direct glucose monitoring.

Medical disclaimer: This A1C calculator is for general information and education only. It is not a diagnosis, treatment plan, or medical advice. A1C and eAG must be interpreted by a qualified healthcare professional alongside your full clinical picture, and any diagnosis of prediabetes or diabetes requires confirmed laboratory testing. Never start, stop, or change medication based on this tool. If you have concerns about your blood sugar, contact your doctor or a licensed clinician.