This calculator converts HbA1c between the NGSP percentage and the IFCC mmol/mol scale using the NGSP master equation. It returns the same result on the other scale. It does not diagnose diabetes, does not assign a category, and does not replace the HbA1c value or range on your report.
What this calculator does
HbA1c is reported on two scales. The NGSP or DCCT scale uses a percentage, and the IFCC scale uses mmol/mol. A laboratory chooses one, and the report usually names it. The two scales describe the same glycated haemoglobin measurement, and the NGSP master equation is the accepted link between them.
This page converts a single value from one scale to the other. It does not estimate average glucose, does not apply a diagnostic threshold, and does not tell you whether the result is normal. The value and the range on the report remain the reference.
The equation
The NGSP master equation, as published by the NGSP:
NGSP (%) = 0.09148 × IFCC (mmol/mol) + 2.152To convert in the other direction:
IFCC (mmol/mol) = (NGSP (%) − 2.152) / 0.09148| Variable | Meaning |
|---|---|
| NGSP (%) | The HbA1c result on the NGSP or DCCT percentage scale. |
| IFCC (mmol/mol) | The HbA1c result on the IFCC scale. |
| 0.09148 | The slope of the master equation. |
| 2.152 | The intercept of the master equation. |
Source: NGSP, IFCC Standardization of HbA1c. The master equation relates the NGSP and IFCC networks.
How to use it
- Find the HbA1c value and the scale on the report. The report may print one scale or both.
- Enter the value and select the scale printed on the report.
- Read the converted value on the other scale. It is the same measurement, expressed differently.
- Keep the original value and scale when you compare reports. A converted value is useful for orientation, not a replacement for the reported result.
What the result means, and what it does not
The result is the same HbA1c measurement on the other scale. It does not add information about glucose, and it does not change the underlying result. A laboratory may round or report the two scales differently, so a small difference after conversion is expected.
The calculator does not assign a diagnostic category, a target, or a risk level. HbA1c is interpreted with other results, history, and the laboratory's range. If the report prints a range or a comment, that is the one that applies.
Limitations
- Rounding. Laboratories may round the percentage or the mmol/mol value, so a converted value can differ slightly from a printed one.
- Assay differences. Different assays and methods can produce small differences in HbA1c, and a conversion does not correct for that.
- Not estimated average glucose. Some reports print an estimated average glucose derived from HbA1c. It is a different quantity and is not part of this conversion.
- Equation updates. The master equation is monitored by the NGSP. This page states the version it uses so the calculation can be checked.
- One value. A conversion does not turn a single HbA1c into a trend or a diagnosis.
What this page is not
This calculator is a unit conversion from a published equation. It is not a diagnosis, a target, a treatment recommendation, or medical advice. It does not replace the HbA1c value, range, or comment on your report. Verify the value and scale against the original report and discuss the result with a qualified professional.