Convert HbA1c between percentage (NGSP) and mmol/mol (IFCC) units with diabetes risk assessment
This calculator is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional.
HbA1c (glycated haemoglobin) is a crucial blood test used to diagnose and monitor diabetes. Unlike a standard blood glucose test that shows your blood sugar at a single moment in time, HbA1c provides an average of your blood sugar levels over the past two to three months. It works by measuring the percentage of haemoglobin -- the protein in red blood cells that carries oxygen -- that has glucose attached to it. In the UK, HbA1c is now reported in mmol/mol (the IFCC standard), having switched from the older percentage system (NGSP standard) in 2011. However, many international resources, apps, and patients still use the percentage system. This converter allows you to easily switch between the two units so you can understand your results regardless of which format they are presented in. The NHS uses HbA1c as the primary test for diagnosing type 2 diabetes. A result of 48 mmol/mol (6.5%) or above indicates diabetes, while 42-47 mmol/mol (6.0-6.4%) indicates pre-diabetes -- a condition where blood sugar levels are higher than normal but not yet high enough to be classified as diabetes. Diabetes UK estimates that around 13.6 million people in the UK are at increased risk of type 2 diabetes.
To convert your HbA1c result: 1. Enter your HbA1c value. This is the number from your blood test result. If your result is a small number (typically 4-14), it is likely in percentage format. If it is a larger number (typically 20-130), it is likely in mmol/mol format. 2. Select the input unit. Choose "% (NGSP)" if your value is in the percentage format, or "mmol/mol (IFCC)" if it is in the international standard format used in the UK. 3. View your converted result. The calculator displays the equivalent value in the other unit system, your estimated average glucose in mmol/L, and your diabetes risk category based on NHS thresholds. 4. Discuss with your healthcare team. If your HbA1c is in the pre-diabetes or diabetes range, speak to your GP about management options. For people already diagnosed with diabetes, an HbA1c target of 48 mmol/mol (6.5%) or below is typically recommended, though individual targets may vary.
The conversion between NGSP (percentage) and IFCC (mmol/mol) units uses the following standardised equations: From % to mmol/mol: mmol/mol = (HbA1c% - 2.152) / 0.09148 From mmol/mol to %: HbA1c% = (mmol/mol x 0.09148) + 2.152 These equations were established by the IFCC working group to provide a precise mathematical relationship between the two measurement systems. For example, 6.5% converts to (6.5 - 2.152) / 0.09148 = 47.5, which rounds to 48 mmol/mol. The calculator also estimates your average blood glucose using the formula: estimated average glucose (eAG) in mmol/L = (HbA1c% x 1.59) - 2.59. This gives you an approximation of what your blood sugar has averaged over the past 2-3 months. Diabetes categories per NHS guidelines: Normal is below 42 mmol/mol (below 6.0%). Pre-diabetes is 42-47 mmol/mol (6.0-6.4%). Diabetes is 48 mmol/mol (6.5%) or above. These thresholds were established based on the level of HbA1c at which the risk of diabetic retinopathy (eye damage) begins to increase significantly.
HbA1c testing has several advantages over fasting glucose tests: it does not require fasting, it reflects long-term blood sugar control rather than a single point in time, and it is less affected by short-term factors such as stress or illness. However, HbA1c may be unreliable in certain conditions that affect red blood cell turnover, such as haemoglobin variants (e.g. sickle cell trait), pregnancy, recent blood transfusion, or chronic kidney disease. For people with diagnosed diabetes, Diabetes UK recommends having your HbA1c checked at least twice a year. If your diabetes is newly diagnosed or your treatment has changed, more frequent testing may be recommended. Most people with type 2 diabetes should aim for an HbA1c of 48 mmol/mol (6.5%) or below, though your healthcare team may set an individual target. Reference: NHS Diabetes information (nhs.uk/conditions/type-2-diabetes), Diabetes UK HbA1c guidance (diabetes.org.uk), NICE Type 2 diabetes guideline NG28.