HbA1c calculator and HbA1c chart in mmol/mol

Reviewed by the JForH team · 2026-10-30

To turn an HbA1c percentage into mmol/mol, take away 2.15 and multiply by 10.929. In the UK, below 42 mmol/mol (6.0%) is normal, 42–47 mmol/mol (6.0–6.4%) is prediabetes and 48 mmol/mol (6.5%) or more is in the diabetes range. An HbA1c of 53 mmol/mol (7.0%) means your blood sugar has averaged about 8.5 mmol/L.

HbA1c chart mmol/mol

Find your HbA1c in the first column. The second column is the same result as a percentage, the old unit. The third is your estimated average blood sugar in mmol/L, the unit your meter or sensor shows.

Every row is worked out from the two formulas below, rounded to a whole number of mmol/mol and one decimal place of mmol/L. A quick rule of thumb from the chart: each 11 mmol/mol (1 percentage point) is about 1.6 mmol/L of average blood sugar.

How do I convert HbA1c mmol/mol to a percentage?

Divide the mmol/mol number by 10.929, then add 2.15. To go the other way, take 2.15 away from the percentage and multiply by 10.929.

• mmol/mol = (% − 2.15) × 10.929
• % = (mmol/mol ÷ 10.929) + 2.15

Say your letter from the surgery says 58 mmol/mol. 58 ÷ 10.929 is 5.31, plus 2.15 gives 7.46, so about 7.5%.

These come from the master equation that links the two lab standards, published by the NGSP (the US body that standardises the percentage) and the IFCC (the international body behind mmol/mol). The NGSP gives it as % = 0.09148 × mmol/mol + 2.152. Turned round and rounded, that is the formula above. It gives the same whole numbers across the chart.

Diabetes UK says mmol/mol has been the standard unit in the UK since 2009. Before that, results were given as a percentage, which is why older leaflets and many websites still use it.

How do I turn HbA1c into average blood sugar in mmol/L?

Multiply the percentage by 1.59 and take away 2.59. The answer is your estimated average glucose in mmol/L.

So 53 mmol/mol (7.0%) gives 1.59 × 7.0 − 2.59 = 8.54, about 8.5 mmol/L. And 75 mmol/mol (9.0%) gives about 11.7 mmol/L.

The formula comes from the ADAG study, published in Diabetes Care in 2008. Researchers compared HbA1c with frequent finger-prick and sensor readings in 507 adults. The calculator on this page also shows mg/dL, the US unit, using the study's other formula (28.7 × % − 46.7).

It is an estimate. Two people with the same HbA1c can have somewhat different true averages, so treat it as a guide.

What is a normal HbA1c in the UK?

Below 42 mmol/mol (6.0%) is normal. These are the bands used in the UK:

American websites often say prediabetes starts at 5.7%. That is about 39 mmol/mol. The UK starts the band higher, at 42, so don't be thrown if a US chart tells you something different.

Is an HbA1c of 42 prediabetes?

Yes. 42 mmol/mol (6.0%) is the bottom of the UK prediabetes range, which runs to 47.

Prediabetes means your blood sugar is higher than normal but not in the diabetes range. It is a warning you can act on. In England, an HbA1c of 42–47 mmol/mol in the last 12 months can make you eligible for the NHS Diabetes Prevention Programme, called Healthier You. Your GP practice can refer you, and some areas let you refer yourself.

Is an HbA1c of 48 diabetes?

48 mmol/mol (6.5%) or over is the level the NHS uses for type 2 diabetes. Your GP will look at it alongside your symptoms and any other results before giving a diagnosis, so ask whether a repeat test is needed.

At 48 mmol/mol, your average blood sugar works out at about 7.7 to 7.8 mmol/L.

What HbA1c should I aim for with type 2 diabetes?

NICE suggests most adults with type 2 diabetes aim for 48 mmol/mol (6.5%). If you take a medicine that can cause hypos, such as a sulfonylurea like gliclazide, the target is usually 53 mmol/mol (7.0%).

• 48 mmol/mol (6.5%): managed by diet and activity, or with a medicine not linked to hypos, such as metformin.
• 53 mmol/mol (7.0%): on a medicine that can cause hypos.
• 58 mmol/mol (7.5%) or more: NICE says your treatment should be stepped up, with support for diet and activity.

These come from the NICE type 2 diabetes guideline, NG28, last updated in February 2026. Your target is agreed with you. Your GP or diabetes nurse may set a looser one if you are frail, older or at risk from hypos.

Is there an HbA1c chart by age?

No. The numbers for normal, prediabetes and diabetes are the same at every adult age.

What changes with age is the target for people who already have diabetes. NICE says targets can be relaxed for older or frail people, and Diabetes UK says the same. That's because a hypo can cause a fall or confusion, and the risk of tight control can outweigh the benefit.

Why doesn't my HbA1c match my meter or sensor?

Because they measure different things. HbA1c is the share of haemoglobin in your red blood cells that has sugar stuck to it. Diabetes UK says it reflects roughly the last 2 to 3 months.

A finger-prick reading is one moment. A few readings a day can miss the highs after meals or the lows at night.

Some conditions that affect red blood cells, such as sickle cell anaemia, thalassaemia and haemolytic anaemia, can make HbA1c less accurate. Diabetes UK suggests asking your doctor about another test if that applies to you.

How often should my HbA1c be checked?

Every 3 to 6 months until it is stable, then every 6 months, according to NICE NG28. Diabetes UK says you are entitled to at least one a year as part of your annual review.

You don't need to fast for an HbA1c. It's a normal blood test, usually done at your GP surgery.

What should I do with my HbA1c result?

Write it down with the date, in mmol/mol, so you can see the trend from one test to the next. Then look at where it sits.

• Below 42: normal. If you are South Asian, Black African or African Caribbean, Diabetes UK says your risk starts from age 25, so keep up your checks.
• 42–47: prediabetes. Ask your GP practice about Healthier You.
• 48 or over without a diagnosis: book a GP appointment to talk it through.
• Above your agreed target: ask your GP or diabetes nurse what to change. A high number tells you the plan needs a change, not that you have failed.

Don't stop or change any diabetes medicine on your own because of one result.

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Last updated: 2026-10-30. Educational information, not medical advice. Talk to your doctor before changing your treatment.