A1C Estimator, GMI Calculator & Glucose Unit Converter

Convert A1C, average glucose, GMI, and international glucose units in one place.

Understand how your lab A1C, average glucose, CGM metrics, GMI, and Time in Range connect. This calculator is for educational use only and does not replace advice from your healthcare provider.

Educational tool

Non-diagnostic

What number do you have?

Learn why A1C and CGM metrics can tell different parts of your glucose story.

What this means

A1C reflects longer-term glucose exposure, while CGM metrics such as GMI and Time in Range explain daily glucose patterns. These numbers are best reviewed together with your healthcare provider.

Understanding the units

A1C can be reported as % or as IFCC mmol/mol. Blood glucose and estimated average glucose are reported as mg/dL or mmol/L. These units are related through conversion formulas, but mmol/L and mmol/mol are not the same unit.

A1C units

% · IFCC mmol/mol

Glucose units

mg/dL · mmol/L

For example, an A1C of 7.0% is about 53 mmol/mol in IFCC A1C units, and it corresponds to an estimated average glucose of about 154 mg/dL or 8.6 mmol/L.

Reference

We use published formulas and public U.S. reference data.
These links are provided so you can see where each calculation comes from.

sources and fomulas

A1C to estimated average glucose (eAG)
eAG mg/dL = 28.7 × A1C – 46.7
This relationship comes from the ADAG study and is also used by NGSP and the ADA Professional eAG/A1C calculator. It translates an A1C percentage into estimated average glucose, eAG, in mg/dL.
eAG is an estimate. It helps relate A1C to glucose meter units, but it is not the same as a single glucose reading.
- NGSP: HbA1c and eAG
- ADA Professional: eAG/A1C Calculator

A1C % to IFCC mmol/mol

- IFCC mmol/mol = 10.93 × A1C% – 23.50
  This conversion is based on the NGSP/IFCC master equation for reporting HbA1c in NGSP/DCCT-aligned percent units and IFCC mmol/mol units.
- NGSP: IFCC Standardization of HbA1c

IFCC mmol/mol to A1C %
A1C% = 0.09148 × IFCC + 2.152
This is the NGSP master equation for converting IFCC HbA1c units, mmol/mol, back to NGSP/DCCT-aligned A1C percent.
- NGSP: IFCC Standardization of HbA1c

GMI (Glucose Management Indicator)
GMI (%) = 3.31 + 0.02392 × CGM mean glucose in mg/dL
This formula comes from the 2018 Diabetes Care paper that introduced Glucose Management Indicator, GMI, as a CGM-based estimate derived from mean glucose.
GMI is an A1C-like estimate based on CGM data. It may not match a laboratory-measured A1C exactly.
- Diabetes Care: GMI Paper
- PubMed Central full text

Blood glucose unit conversion
mmol/L = mg/dL / 18.018
mg/dL = mmol/L × 18.018
These are standard glucose unit conversions between mg/dL and mmol/L. They are used to convert blood glucose or estimated average glucose values, not A1C itself.
mg/dL and mmol/L are glucose units. A1C units are % or IFCC mmol/mol.
- NCBI Bookshelf: Glucose unit conversion table

U.S. A1C comparison
Data source: NHANES August 2021–August 2023
Variables: LBXGH (A1C %), DIQ010 (diagnosed diabetes), WTPH2YR (phlebotomy 2-year weight), RIDAGEYR (age)
The U.S. comparison feature uses adults age 20 and older with valid A1C values and positive phlebotomy weights. Percentiles are calculated as the weighted percentage of people in the selected NHANES reference group with A1C less than or equal to the user’s A1C.
This comparison is educational and should not be used to judge your health or treatment plan.

Frequently asked questions

What is the difference between A1C and GMI?

Can GMI replace a lab A1C test?

Why is my GMI different from my A1C?

Disclaimer

This calculator is for educational purposes only and is not intended to diagnose, treat, or replace professional medical advice. A1C results may be affected by certain conditions such as anemia, kidney disease, liver disease, hemoglobin variants, blood loss, transfusion, pregnancy, and certain medications. Always discuss your results and personal goals with your healthcare provider.