ADAG study (Diabetes Care 2008): eAG (mg/dL) = 28.7 × A1C − 46.7. Or in mmol/L: eAG (mmol/L) = 1.59 × A1C − 2.59. To go backwards: A1C = (eAG + 46.7) / 28.7. The ADAG study correlated continuous glucose monitor readings over 3 months against lab A1C in 507 participants.

What are the diagnostic thresholds?

Normal: A1C < 5.7% (eAG < 117 mg/dL / 6.5 mmol/L). Prediabetes: 5.7-6.4% (eAG 117-140 / 6.5-7.8). Diabetes: ≥6.5% (eAG ≥140 / ≥7.8). Diabetes target (most): A1C < 7%. Stricter target (young, healthy): < 6.5%. Looser target (elderly, frail, hypoglycemia risk): < 8%.

Why does my A1C disagree with my fingerstick average?

Several reasons: (1) A1C reflects 90-120 day average; fingerstick captures only when you check (often pre-meal lows). (2) Iron deficiency, kidney disease, hemoglobin variants, and recent transfusion can falsely lower A1C. (3) Glycemic variability — same average from stable vs spiky patterns. CGM (continuous glucose monitor) data typically aligns better with A1C than fingerstick.

How fast does A1C change?

Roughly: 50% of A1C reflects the last 30 days, 25% the previous 30 days, 25% the 60 days before that. So a glucose-control change shows up at ~30% of full effect at 1 month, ~75% at 2 months, ~95% at 3 months. Re-test A1C every 3 months when adjusting therapy.

Are there other conversion formulas?

Yes — older formulas (e.g., DCCT) gave slightly different numbers. The ADAG formula is now the international standard endorsed by ADA, EASD, IDF, and the IFCC. Some labs report 'eAG' alongside A1C using this same formula.

A1C ↔ Average Blood Glucose Converter

Health & Fitness· 18 tools

Free A1C-to-glucose converter. Convert HbA1c percentage to estimated average glucose (eAG) in mg/dL or mmol/L using the validated ADAG formula. Useful for diabetes management, comparing fingerstick averages to A1C lab results, and understanding A1C in everyday glucose terms (e.g., A1C 7% ≈ average 154 mg/dL ≈ 8.6 mmol/L).

HbA1c (%)

ADAG formula · eAG (mg/dL) = 28.7 × A1C − 46.7

Normal < 5.7% · Prediabetes 5.7-6.4% · Diabetes ≥ 6.5%

Iron deficiency, kidney disease, hemoglobin variants can falsely lower A1C.

A1C

6.5%

Diabetes range

eAG (mg/dL)

140

eAG (mmol/L)

7.8

A1C / eAG reference table

A1C %	eAG mg/dL	eAG mmol/L	Category
5.0%	97	5.4	Normal
5.7%	117	6.5	Prediabetes
6.0%	125	7.0	Prediabetes
6.5%	140	7.8	Diabetes range
7.0%	154	8.6	Diabetes range
8.0%	183	10.2	Diabetes range
9.0%	212	11.8	Diabetes range
10.0%	240	13.4	Diabetes range
12.0%	298	16.5	Diabetes range

Disclaimer: For informational purposes only. This is not medical advice — consult a qualified healthcare provider for personal recommendations.

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