Type a blood glucose value in either mg/dL or mmol/L and the other unit follows instantly, labelled with the range it falls in for a fasting reading, a two-hour glucose tolerance test or a random check. The second half converts HbA1c between the NGSP percentage used in the US, the IFCC mmol/mol figure used across most of Europe, and estimated average glucose in either unit — all four boxes linked, so you can start from whichever number your lab gave you. Everything runs in your browser, so no reading you type is ever sent anywhere. If you are working through related numbers, the BMI calculator and the macro calculator may be useful alongside it.
Blood sugar Calculator
mg/dL to mmol/L and A1C to average glucose, both directions, with the published range each value falls in.
Blood glucose reading
Type in either box and the other follows. The reading type only changes which published range the value is compared against.
HbA1c and average glucose
All four boxes are linked — type in any one. These average-glucose figures cover roughly the last 2–3 months, so they are not comparable to the single reading above.
Your reading
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Published range—
Your A1C
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Published range—
A1C conversion table
Ranges are the diagnostic cut points published in the ADA Standards of Care in Diabetes — 2026. They are reference figures, not a diagnosis: diagnosis needs a repeat confirmatory test and a clinician who knows your history.
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Why there are two numbers for one thing
Blood glucose is a concentration, and the world never agreed on how to express it. The United States, Germany, Japan and a handful of other countries report it as a mass concentration — milligrams of glucose per decilitre of blood. The United Kingdom, Ireland, most of Europe, Australia, New Zealand and Canada report it as a molar concentration — millimoles per litre. Same blood, same glucose, different unit.
Converting between them is exact, because it depends only on the molar mass of glucose. Glucose is C6H12O6, which weighs 180.156 grams per mole, so one millimole per litre is 180.156 milligrams per litre, or 18.0156 milligrams per decilitre. To go from mg/dL to mmol/L, divide by 18.0156. To go the other way, multiply. Plenty of references round this to a flat 18 — the difference is under a tenth of a percent, which never changes a clinical decision, but this calculator uses the full figure.
A1C is a different measurement, not a different unit
A glucose reading is a snapshot: it tells you what your blood sugar was at the moment the drop hit the strip, and it moves constantly with meals, exercise, illness and stress. HbA1c measures something else entirely. Glucose in the bloodstream sticks irreversibly to haemoglobin inside red blood cells, and because those cells live around three months, the proportion of haemoglobin carrying a sugar molecule reflects average exposure over roughly the last two to three months — weighted towards the most recent weeks, since younger cells outnumber older ones.
That is why the two halves of this calculator are kept separate. You cannot convert this morning’s fingerstick into an A1C, and an A1C cannot tell you what your glucose is right now. What you can do is express an A1C in glucose units, which is what estimated average glucose does.
The three A1C scales
NGSP (%) is the percentage figure familiar in the US, traceable to the Diabetes Control and Complications Trial. IFCC (mmol/mol) is the SI-based scale used across most of Europe and much of the rest of the world, reported as millimoles of glycated haemoglobin per mole of haemoglobin. The two are linked by the NGSP master equation: NGSP % = 0.09148 × IFCC + 2.152. An A1C of 7.0% is 53 mmol/mol; 6.5% is 48; 5.7% is 39.
Estimated average glucose (eAG) is the third way of saying it, expressed in the same mg/dL or mmol/L a meter shows. It comes from the 2008 A1C-Derived Average Glucose study, which tracked 507 people across ten countries with continuous monitors and frequent fingersticks for three months and fitted the line eAG (mg/dL) = 28.7 × A1C − 46.7. An A1C of 7.0% works out to roughly 154 mg/dL, or 8.6 mmol/L.
The ranges this calculator compares against
The labels come from the diagnostic cut points in the American Diabetes Association’s Standards of Care in Diabetes — 2026:
- Fasting plasma glucose (no calories for at least eight hours) — under 100 mg/dL (5.6 mmol/L) is normal, 100 to 125 mg/dL (5.6–6.9 mmol/L) is impaired fasting glucose, and 126 mg/dL (7.0 mmol/L) or above meets the diabetes threshold.
- Two-hour plasma glucose during a 75 g oral glucose tolerance test — under 140 mg/dL (7.8 mmol/L) is normal, 140 to 199 mg/dL (7.8–11.0 mmol/L) is impaired glucose tolerance, and 200 mg/dL (11.1 mmol/L) or above meets the threshold.
- A1C — under 5.7% (39 mmol/mol) is normal, 5.7 to 6.4% (39–47 mmol/mol) is prediabetes, and 6.5% (48 mmol/mol) or above meets the threshold.
- Random glucose only counts diagnostically at 200 mg/dL (11.1 mmol/L) or above, and only when classic symptoms of hyperglycaemia are present.
Two things matter about these numbers. First, a single result never diagnoses anything on its own — apart from an unequivocal hyperglycaemic crisis, the ADA requires a confirmatory second test. Second, the three tests do not agree with each other perfectly; they measure different aspects of glucose metabolism, and a person can land in the prediabetes range on one and the normal range on another.
Going the other way, and hypoglycaemia
The low end has its own thresholds, and they apply whatever kind of reading you took. The ADA sets the hypoglycaemia alert value at 70 mg/dL (3.9 mmol/L) — low enough to treat with fast-acting carbohydrate and retest after fifteen minutes. Below 54 mg/dL (3.0 mmol/L) is classed as clinically significant hypoglycaemia. This calculator flags both, and those flags override the fasting and OGTT ranges, because a low reading is a low reading regardless of when you took it.
When A1C stops being reliable
Because A1C depends on red blood cells living a predictable three months, anything that changes their lifespan distorts the result. Conditions that shorten it — haemolytic anaemia, recent significant blood loss, transfusion, some haemoglobin variants — pull A1C down and make control look better than it is. Conditions that lengthen it, such as iron or B12 deficiency or splenectomy, push it up. Pregnancy, chronic kidney disease and advanced liver disease all shift it too. In those situations glucose measurements and continuous monitoring data are more trustworthy than the A1C number, and the eAG conversion here inherits the same limitation.
Even in a straightforward case, eAG is a population average fitted to a line, not your personal calibration. Individual variation of ten to twenty percent around the fitted value is common, which is the usual explanation when someone’s meter average and their lab A1C tell slightly different stories.
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Frequently asked questions
How do I convert mg/dL to mmol/L?
Divide by 18.0156. That figure is the molar mass of glucose (180.156 g/mol) expressed per decilitre, so the conversion is exact rather than approximate. To go from mmol/L back to mg/dL, multiply by 18.0156. Many references round it to 18, which shifts the answer by less than a tenth of a percent.
What is 7% A1C in mmol/mol and in blood sugar?
An A1C of 7.0% is 53 mmol/mol on the IFCC scale, and corresponds to an estimated average glucose of about 154 mg/dL, or 8.6 mmol/L. The IFCC figure comes from the NGSP master equation and the average glucose from the ADAG study equation, eAG = 28.7 × A1C − 46.7.
Can I convert a single glucose reading into an A1C?
Not meaningfully. A1C reflects average glucose over about two to three months, so it takes sustained readings to move it. One fingerstick tells you nothing about that average — a normal morning reading is perfectly compatible with a high A1C, and vice versa. This calculator keeps the two separate for that reason, and only converts A1C against an <em>average</em> glucose figure.
What blood sugar level is considered diabetes?
Under the ADA criteria, a fasting plasma glucose of 126 mg/dL (7.0 mmol/L) or above, a two-hour value of 200 mg/dL (11.1 mmol/L) or above during a 75 g glucose tolerance test, or an A1C of 6.5% (48 mmol/mol) or above. A random reading of 200 mg/dL or above also counts, but only alongside classic symptoms. Except in an unequivocal hyperglycaemic crisis, a diagnosis requires a confirmatory repeat test.
What counts as low blood sugar?
The ADA sets the alert value at 70 mg/dL (3.9 mmol/L), and treats anything below 54 mg/dL (3.0 mmol/L) as clinically significant hypoglycaemia. Both thresholds apply regardless of when the reading was taken, which is why this calculator flags them ahead of the fasting and tolerance-test ranges.
Why does my meter average not match my lab A1C?
Several reasons, and they compound. The ADAG equation is a population fit, so individual variation of ten to twenty percent around it is normal. Your meter average only reflects the moments you chose to test — if you mostly test fasting, it will understate your true 24-hour average. And any condition that changes red blood cell lifespan, from iron deficiency to recent blood loss, shifts A1C independently of your actual glucose.
Is NGSP or IFCC the right A1C number?
Both are correct; they are the same measurement on two scales. The US reports NGSP percentages, most of Europe reports IFCC in mmol/mol, and many countries now report both alongside estimated average glucose. They are linked exactly by NGSP % = 0.09148 × IFCC + 2.152, so neither carries more information than the other.
Does this calculator diagnose diabetes?
No. It converts between units and tells you which published ADA range a value falls in — that is arithmetic and a lookup, not a diagnosis. Diagnosis needs a repeat confirmatory test, and interpretation needs a clinician who knows your history, medication and other results.