Haemoglobin Unit Converter
Haemoglobin Unit Converter
Convert haemoglobin between g/dL, g/L and mmol/L — using the globin monomer mass, which is why SI reports read 8 to 11 mmol/L rather than 2 to 3.
Haemoglobin converter
Mass ⇄ molarHaemoglobin 13.8 g/dL
Formulae and conversion factors
mmol/L = g/dL × 0.620559
g/dL = mmol/L ÷ 0.620559
- 0.620559
- derived from the haemoglobin MONOMER mass: 10 g/L per g/dL ÷ 16,114.5 g/mol × 1,000 mmol per mol
- 16,114.5 Da
- the mass of one globin subunit with its haem group. The assembled tetramer is 64,458 Da, and using it gives a molar result four times too low
- × 10
- g/dL to g/L is a decimal shift with no molecular weight involved — the same measurement expressed per litre rather than per decilitre
Worked example
Haemoglobin 13.8 g/dL
13.8 × 10 = 138 g/L
13.8 × 0.620559 = 8.56 mmol/L
Converting with the 64,458 Da tetramer instead would give 2.14 mmol/L — four times too low
The same haemoglobin in all three units
| g/dL | g/L | mmol/L | Note |
|---|---|---|---|
| 7.0 | 70 | 4.34 | Common transfusion threshold in a stable patient |
| 8.0 | 80 | 4.96 | — |
| 10.0 | 100 | 6.21 | — |
| 12.0 | 120 | 7.45 | WHO anaemia threshold, non-pregnant women |
| 13.0 | 130 | 8.07 | WHO anaemia threshold, men |
| 14.0 | 140 | 8.69 | — |
| 15.0 | 150 | 9.31 | Upper reference limit, women |
| 17.0 | 170 | 10.55 | Upper reference limit, men |
| 20.0 | 200 | 12.41 | Erythrocytosis — investigate |
Three units, and one conversion that is regularly got wrong
Haemoglobin is reported in three units and all three are in daily use. Grams per decilitre is the form printed by most laboratories in the United Kingdom, Ireland and North America; grams per litre is the same measurement multiplied by ten and is the commonest SI form worldwide; and millimoles per litre is used routinely in the Netherlands, Denmark and parts of Scandinavia. The first conversion is a decimal shift, but the molar one is not, and it is where results are most often misread.
The molar factor rests on the mass of a single globin subunit, 16,114.5 Da, and not on the 64,458 Da mass of the assembled tetramer. Haemoglobin carries four globin chains and four haem groups, and clinical SI reporting expresses the concentration of haem-carrying monomer rather than of whole molecules. That is the entire reason a healthy man reads roughly 8 to 11 mmol/L on a Dutch or Danish report. Converting with the tetramer mass produces a figure four times too small, around 2 to 3 mmol/L, which looks catastrophically anaemic and is simply an arithmetic error.
The WHO thresholds for anaemia are 13 g/dL in adult men and 12 g/dL in non-pregnant adult women, which are 130 and 120 g/L, or 8.07 and 7.45 mmol/L. Those three pairs make a quick sanity check on any conversion: a molar figure near 8 for a man sits at the anaemia threshold, whereas a figure near 2 means the tetramer mass has been used.
Whichever unit it is expressed in, haemoglobin is a concentration rather than a measure of red cell mass, and it is diluted by whatever plasma volume happens to be present. It falls in pregnancy through physiological plasma expansion, and in fluid overload or generous crystalloid resuscitation, without a single red cell having been lost — which is part of why a lower threshold is used in pregnancy. It rises in dehydration, and it can look reassuringly normal in the first hours after a major haemorrhage, before fluid shifts have restored the plasma volume. Read the number alongside volume status rather than on its own.
Frequently asked questions
How do I convert haemoglobin from g/dL to mmol/L?
Multiply by 0.620559. A haemoglobin of 13.8 g/dL is 8.56 mmol/L. The factor uses the globin monomer mass of 16,114.5 Da, which is the convention in clinical SI reporting.
Why do Dutch and Danish reports show haemoglobin around 9 mmol/L?
Because the molar concentration is expressed per globin monomer, not per tetramer. A healthy adult reads roughly 8 to 11 mmol/L on that basis. A conversion done with the 64,458 Da tetramer gives about a quarter of that and is wrong.
How do I convert g/dL to g/L?
Multiply by 10 — a haemoglobin of 13.8 g/dL is 138 g/L. No molecular weight is involved; it is the same measurement expressed per litre instead of per decilitre.
What are the WHO haemoglobin thresholds for anaemia?
Below 13 g/dL in adult men and below 12 g/dL in non-pregnant adult women, which are 8.07 and 7.45 mmol/L respectively. Lower thresholds apply in pregnancy and in young children.
Can haemoglobin change without a change in red cell mass?
Yes. It is a concentration, so plasma volume moves it. It falls with the plasma expansion of pregnancy and with fluid overload, and rises with dehydration, in each case without red cells having been gained or lost.
Related calculators
References
- World Health Organization. Haemoglobin concentrations for the diagnosis of anaemia and assessment of severity. Vitamin and Mineral Nutrition Information System. Geneva: WHO.
- Bain BJ, Bates I, Laffan MA, eds. Dacie and Lewis Practical Haematology. Elsevier — haemoglobinometry and reference intervals.