HbA1c conversion: % to mmol/mol

HbA1c converts by an equation rather than a factor, because the two scales do not share a zero: mmol/mol = 10.929 × (% − 2.15), and in reverse % = mmol/mol ÷ 10.929 + 2.15.

Common values

% to mmol/mol

HbA1c, % to mmol/mol
%	mmol/mol
4	20
5	31
5.5	37
5.7	39
6	42
6.5	48
7	53
7.5	58
8	64
9	75
10	86
12	108

mmol/mol to %

HbA1c, mmol/mol to %
mmol/mol	%
20	4.0
30	4.9
35	5.4
40	5.8
45	6.3
50	6.7
55	7.2
60	7.6
70	8.6
80	9.5
90	10.4
100	11.3

Each converted value is worked out in full and then rounded: mmol/mol to whole numbers and % to one decimal place.

Sources: the master equation, Hoelzel W and colleagues, Clin Chem 2004;50:166-174, and mmol/mol in place of the IFCC percentage, Consensus Committee, Diabetes Care 2007;30:2399-2400.

A study tool, not a clinical one

This page exists for converting HbA1c between % and mmol/mol, and learning where the equation between the two units comes from. It is not clinical decision support and must not be used to treat anybody.

Read a result against its own report. Laboratories differ in method and in the population they set reference intervals from, so interpret a converted number against the ranges printed on the report it came from.
The equation describes assay results. Below 2.15 % it gives a negative mmol/mol, so it says nothing about a number outside the range an assay reports.
Every calculation here is shown, not hidden. If a step does not match what you were taught, follow the working rather than the output, and tell us if we have it wrong. How the pages are checked is set out in the editorial policy.

Why HbA1c converts by an equation

The two units count different things. The percentage is the NGSP scale, aligned to the DCCT trial, and mmol/mol is the IFCC reference method’s count of millimoles of HbA1c per mole of hemoglobin. The IFCC master equation relates them as % = 0.0915 × mmol/mol + 2.15, and solved for mmol/mol that is mmol/mol = 10.929 × (% − 2.15), 10.929 being 1 ÷ 0.0915 to five figures.

So a percentage cannot be multiplied across. 6.5 % × 10.929 is 71, where the equation gives 48 mmol/mol: the 2.15 has to come off first.

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

Which countries report which unit

American and Canadian laboratories report HbA1c as an NGSP percentage. British laboratories report the IFCC unit, mmol/mol, and Australian ones report both.

Worked examples

6.5 % in mmol/mol
= 10.929 × (6.5 − 2.15)
= 47.5412 mmol/mol

48 mmol/mol in %
= 48 ÷ 10.929 + 2.15
= 6.54198 %