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A1C Calculator

Convert between A1C percentage and estimated average glucose in either direction, with the standard category ranges.

Written by Jude Ramsey · Last updated August 2026 · How these calculators are checked

The method behind this calculator

A1C measures the share of haemoglobin that has glucose attached to it, which reflects average blood sugar over roughly the previous two to three months. The ADA conversion turns that percentage into an estimated average glucose you can compare against meter readings.

Because A1C is an average, it hides swings. Two people with the same A1C can have very different day-to-day variability, which is why continuous monitoring adds information a single number cannot.

Worked example

Worked through, a convert from of A1C percentage produces a result of 6.5%. Underneath, A1C comes out at 6.5% and Average glucose at 140 mg/dL. Change any field and every figure updates as you type.

How to use it

  1. Choose whether you are converting from A1C or from average glucose.
  2. Enter the value and pick your glucose units.
  3. Read the converted figure and the category it falls in.

Formula reference

eAG (mg/dL) = 28.7 × A1C − 46.7 mmol/L = mg/dL ÷ 18.0182 · IFCC mmol/mol = (A1C − 2.15) × 10.929

Questions people ask about this

What is a normal A1C?
Below 5.7% is generally considered normal, 5.7–6.4% is the prediabetes range, and 6.5% or above is in the diabetes range.
How often should A1C be checked?
Typically every three to six months for people managing diabetes, though your clinician sets the interval.
Can A1C be misleading?
Yes — anaemia, recent blood loss, pregnancy and some haemoglobin variants can distort the result. This tool is for general information, not diagnosis.

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