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HbA1c Converter

Converts HbA1c between NGSP percent and IFCC mmol/mol, and shows the estimated average glucose in both mg/dL and mmol/L.

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In short HbA1c is reported two ways and they are not the same scale. NGSP (or DCCT) reports a percentage — 6.5% — and IFCC reports millimoles per mole — 48 mmol/mol. They are related by IFCC = (NGSP − 2.15) × 10.929, which is a straight line with an intercept, so no single multiplier converts between them: multiplying 6.5 by 10.929 gives 71, and the right answer is 48. The UK, Ireland, Australia and much of Europe moved to IFCC reporting in 2011; the United States did not, which is why the same sample is described as 6.5 in one country and 48 in another. A third figure often appears alongside them — estimated average glucose, from the ADAG study regression eAG = 28.7 × NGSP − 46.7 — and that one is genuinely an estimate rather than a conversion, because it is a population average from continuous glucose monitoring, and two people with the same HbA1c can have measurably different mean glucose.

How to use the HbA1c Converter

  1. Type your HbA1c result.
  2. Choose which unit it was reported in — the percentage or mmol/mol.
  3. Read the same result in all four forms, with a reference table beneath.

About the HbA1c Converter

The HbA1c Converter converts HbA1c between NGSP percent and IFCC mmol/mol, and shows the estimated average glucose in both mg/dL and mmol/L. It runs as plain JavaScript inside the page, which means there is no upload step, no queue and no size limit imposed by a server — the only limit is your own device.

What people use it for

  • Reading a result issued in IFCC units when you are used to percentages, or the reverse.
  • Comparing an old report with a new one after moving country.
  • Understanding the estimated average glucose figure printed next to an HbA1c.

Details

NGSP / DCCTA percentage. Used in the United States and several other countries
IFCCmmol/mol. Adopted by the UK, Ireland, Australia and much of Europe in 2011
The equationIFCC = (NGSP − 2.15) × 10.929 — exact and reversible in both directions
6.5% is48 mmol/mol, and an estimated average glucose of 140 mg/dL (7.8 mmol/L)
7.0% is53 mmol/mol, and an estimated average glucose of 154 mg/dL (8.6 mmol/L)
eAGA regression from the ADAG study — an estimate, not a unit conversion
PrivacyThe arithmetic runs in your browser. Nothing you type is sent anywhere

The maths behind it

This tool uses IFCC mmol/mol = (NGSP % − 2.15) × 10.929, and estimated average glucose in mg/dL = 28.7 × NGSP % − 46.7. The first is exact and reversible; the second is a regression from the ADAG study, which is why it is an estimate. Every intermediate value is shown on screen, so the result can be checked by hand.

The NGSP-to-IFCC conversion is exact arithmetic and reverses perfectly. The estimated average glucose is not exact and is not a unit conversion at all — it is an empirical average, shown here because reports show it, and labelled as an estimate because that is what it is.

Where this tool stops

The equations are defined over roughly 4% to 20% NGSP; outside that the tool says so rather than extrapolating quietly. It converts units and does not interpret results — anaemia, recent transfusion, pregnancy and haemoglobin variants all affect what an HbA1c means, and none of that is arithmetic.

Frequently asked questions

Why can I not just multiply by 10.929?
Because the relationship has an intercept. IFCC = (NGSP − 2.15) × 10.929, so the 2.15 has to come off first. Multiplying 6.5 straight by 10.929 gives 71 mmol/mol; the correct answer is 48. That subtraction is the single most common error in converting HbA1c by hand.
Is 48 the same as 6.5?
Yes — 48 mmol/mol in IFCC units and 6.5% in NGSP units are the same measurement written two ways. The pairs worth remembering are 42 for 6.0%, 48 for 6.5%, 53 for 7.0% and 64 for 8.0%.
Why did my country change the units?
IFCC units are traceable to a reference measurement method, while the NGSP percentage is anchored to the assay used in a 1990s trial. The UK, Ireland, Australia and much of Europe switched in 2011 for that reason; the United States kept the percentage because it is what its guidelines and its patients already used.
Is estimated average glucose the same as my meter average?
Not necessarily, and it is not meant to be. eAG comes from a regression fitted across many people in the ADAG study, so it describes the average person with your HbA1c rather than you specifically. Red cell lifespan, anaemia and haemoglobin variants all shift the relationship, which is why the figure is labelled estimated.
Does this tool tell me whether my HbA1c is good?
No. It converts between the units a result can be written in and stops there. Targets differ between guidelines, between countries and between individuals, and they are a conversation for the clinician who ordered the test.
Are there any usage caps on the HbA1c Converter?
No charge and no sign-up. There is no free tier to run out of because there is no paid tier — inputtesthub.com is funded by advertising rather than by metering the utility.
Is my data uploaded anywhere?
No. The HbA1c Converter runs entirely in your browser using JavaScript. Nothing is transmitted, logged or stored, which you can verify yourself in the Network tab of your browser's developer tools.
Can I check the maths myself?
It uses IFCC mmol/mol = (NGSP % − 2.15) × 10.929, and estimated average glucose in mg/dL = 28.7 × NGSP % − 46.7. The first is exact and reversible; the second is a regression from the ADAG study, which is why it is an estimate. The full working is printed under the result, so you can follow every step rather than trusting a black box.
Who is the HbA1c Converter for?
In practice it gets used for three things: reading a result issued in IFCC units when you are used to percentages, or the reverse. Comparing an old report with a new one after moving country. Understanding the estimated average glucose figure printed next to an HbA1c. It is built for exactly those cases rather than being a general-purpose tool with this bolted on.
Where does the HbA1c Converter stop being reliable?
The equations are defined over roughly 4% to 20% NGSP; outside that the tool says so rather than extrapolating quietly. It converts units and does not interpret results — anaemia, recent transfusion, pregnancy and haemoglobin variants all affect what an HbA1c means, and none of that is arithmetic. Knowing where a tool stops being trustworthy matters more than the cases where it works.
What are the key numbers for the HbA1c Converter?
NGSP / DCCT is A percentage. Used in the United States and several other countries. IFCC is mmol/mol. Adopted by the UK, Ireland, Australia and much of Europe in 2011. The equation is IFCC = (NGSP − 2.15) × 10.929 — exact and reversible in both directions. These are printed on the page itself, so you do not have to take them on trust.
Can I rely on this for exact work?
The calculation runs in double precision and the result is shown to ten significant figures, so converting a value and converting it back returns the original. What is displayed is rounded for readability; what is copied is not.

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