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- [A1C calculator](/a1c-calculator) is our most complete page: A1C to average glucose, the full A1C chart, and normal, prediabetes and diabetes ranges.
- [GMI calculator](/gmi-calculator) converts the average glucose from a continuous glucose monitor (CGM) into a Glucose Management Indicator, an A1C-like number, and explains why GMI and a lab A1C from the same period can differ.
Which diabetes tool do you need?
Blood sugar results come in several forms – a single glucose reading, a long-term A1C, insulin levels, or an index of insulin resistance – and in two unit systems. Here is how the tools in this section fit together:
- [A1C calculator and chart](/a1c-calculator) – the most-used tool on AskDr. Convert an A1C percentage to estimated average glucose in mg/dL and mmol/L, see the A1C chart, and check whether a value is in the normal, prediabetes or diabetes range.
- [HbA1c mmol/mol to % converter](/hba1c-mmol-mol-to-percent) – for results reported in IFCC units (mmol/mol), common in the UK, Europe and Australia.
- [Blood sugar converter](/blood-sugar-mg-dl-to-mmol-l) – convert glucose meter, CGM or lab readings between mg/dL and mmol/L.
- [Insulin converter](/insulin-uiu-ml-to-pmol-l) – convert fasting insulin between µIU/mL and pmol/L.
- [HOMA-IR calculator](/homa-ir-calculator) – estimate insulin resistance from fasting glucose and insulin.
Key diabetes thresholds at a glance
| Test | Normal | Prediabetes | Diabetes |
|---|---|---|---|
| A1C | below 5.7% (39 mmol/mol) | 5.7–6.4% (39–46 mmol/mol) | 6.5% (48 mmol/mol) or higher |
| Fasting glucose | below 100 mg/dL (5.6 mmol/L) | 100–125 mg/dL (5.6–6.9 mmol/L) | 126 mg/dL (7.0 mmol/L) or higher |
| 2-hour OGTT glucose | below 140 mg/dL (7.8 mmol/L) | 140–199 mg/dL (7.8–11.0 mmol/L) | 200 mg/dL (11.1 mmol/L) or higher |
These are the American Diabetes Association criteria. The UK's NICE uses 42–47 mmol/mol (6.0–6.4%) to identify people at high risk. A diagnosis of diabetes needs confirmation with a repeat test unless there are clear symptoms with a very high glucose.
How the tests relate to each other
Glucose is a snapshot of blood sugar at one moment. It changes with meals, activity, stress and sleep. A1C reflects average glucose over the previous two to three months, because glucose attaches to haemoglobin in red blood cells over their lifespan. The ADAG study linked the two: each 1 percentage point of A1C corresponds to roughly 29 mg/dL (1.6 mmol/L) of average glucose. An A1C of 7% matches an average of about 154 mg/dL (8.6 mmol/L).
Insulin and HOMA-IR look at a different question – how hard the pancreas is working to keep glucose normal. Insulin resistance often develops years before glucose or A1C rise, which is why HOMA-IR is sometimes used in research and in assessing conditions such as polycystic ovary syndrome. It is not used to diagnose diabetes.
Choosing between mg/dL and mmol/L
The US uses mg/dL for glucose; most other countries use mmol/L. To convert, divide mg/dL by 18 (or multiply mmol/L by 18). Common reference points are 70 mg/dL = 3.9 mmol/L, 100 = 5.6, 126 = 7.0, 180 = 10.0 and 200 = 11.1. A1C has its own pair of units – percent and mmol/mol – linked by a master equation rather than a single factor.
Targets for people with diabetes
Targets are individual, but common reference points are:
- A1C: below 7% (53 mmol/mol) for many adults, with tighter or looser targets depending on hypoglycaemia risk, age and other conditions.
- Time in range on CGM: more than 70% of readings between 70 and 180 mg/dL (3.9–10.0 mmol/L), with less than 4% below 70 mg/dL.
- Pre-meal glucose: 80–130 mg/dL (4.4–7.2 mmol/L) in ADA guidance.
When to seek medical advice
Talk to a clinician if your A1C or fasting glucose is in the prediabetes or diabetes range, or if you have symptoms such as increased thirst, frequent urination, unexplained weight loss or blurred vision. Seek urgent care for glucose readings below 54 mg/dL (3.0 mmol/L) that do not respond to treatment, or above about 300 mg/dL (16.7 mmol/L) with vomiting, abdominal pain, rapid breathing or drowsiness.
Frequently asked questions
Which test is best for diagnosing diabetes?
A1C, fasting glucose and the oral glucose tolerance test are all accepted. A1C is convenient because it does not require fasting, but it can be misleading with anaemia, some haemoglobin variants, kidney disease and pregnancy.
What is a normal A1C?
Below 5.7% (39 mmol/mol). The [A1C chart](/a1c-calculator) shows every common value with its average glucose.
Can I calculate my A1C from my meter readings?
You can estimate it from a long-term average glucose, but meter averages over-represent the times you test. CGM data give a better estimate, called the Glucose Management Indicator (GMI).