Hematocrit to Hemoglobin Ratio Calculator

Background.

Hemoglobin and hematocrit are two views of the same red cells. Hemoglobin is the mass of oxygen-carrying protein in a decilitre of blood; hematocrit is the share of the blood's volume that red cells occupy. Because each red cell is normally filled with hemoglobin to a fairly constant concentration, the two numbers travel together, and clinicians lean on a shortcut called the rule of three: hematocrit in percent is roughly three times hemoglobin in g/dL. A hemoglobin of 14 g/dL goes with a hematocrit near 42%.

Dividing one by the other tests that shortcut. The ratio Hct ÷ Hgb is exactly 100 divided by the mean corpuscular hemoglobin concentration, or MCHC, the average concentration of hemoglobin inside the red cells. A ratio of 3 corresponds to an MCHC of 33.3 g/dL. When cells are pale and under-filled, as in iron deficiency, the ratio drifts above 3; when they are unusually dense, as in hereditary spherocytosis, it drifts below.

What the ratio cannot do is tell you whether someone is anaemic. Dehydration, pregnancy and altitude change how many red cells sit in each decilitre, but they move hemoglobin and hematocrit in step, so on their own they barely shift the ratio. Someone with a hemoglobin of 7 g/dL and a hematocrit of 21% has a perfectly ordinary ratio of 3 and a severe anaemia.

Most automated analyzers measure hemoglobin directly but calculate hematocrit from the red-cell count and mean cell volume, so a ratio far from 3 can also signal a measurement problem rather than a change in the cells. The number is a consistency check and a clinical aid, not a diagnosis.

What is hematocrit to hemoglobin ratio calculator?

The hematocrit-to-hemoglobin ratio is the hematocrit, expressed as a percentage of blood volume, divided by the hemoglobin concentration in grams per decilitre. It has no unit of its own and its value depends entirely on the units used: the familiar figure of about 3 holds only for percent over g/dL. Algebraically it is 100 divided by the MCHC, so it describes how densely the red cells are packed with hemoglobin.

How to use this calculator.

1. 01Copy the Hematocrit from the complete blood count as a percentage. If the report gives it as a fraction such as 0.42 L/L, multiply by 100.
2. 02Copy the Hemoglobin in g/dL. A report in g/L needs dividing by 10, so 140 g/L becomes 14 g/dL; a report in mmol/L needs dividing by 0.6206.
3. 03Take both values from the same blood sample. A hemoglobin from one day paired with a hematocrit from another can produce a ratio that means nothing.
4. 04Check the ratio against the MCHC printed on the same report: 100 divided by the ratio should reproduce it closely, and a mismatch usually points to a unit or transcription error.

The formula.

Ratio = hematocrit (%) ÷ hemoglobin (g/dL). Both inputs measure red-cell material in the same blood: hematocrit is red-cell volume per 100 volumes of blood, and hemoglobin is grams of hemoglobin per decilitre of blood. Dividing one by the other cancels the blood volume and leaves red-cell volume per gram of hemoglobin, which works out to 100 ÷ MCHC. That is why the number is indifferent to how diluted or concentrated the blood is, yet sensitive to how full each red cell is. The page computes the ratio exactly and reports it to twelve significant figures. It does not flag results above or below 3, because the rule of three is a bedside approximation rather than a validated cut-off. Both values must be positive, and hematocrit cannot exceed 100%.

A worked example.

Frequently asked questions.

References& sources.

1. [1]ICSH, Recommendations for reference method for haemoglobinometry in human blood (BIBLIOGRAPHIC).
2. [2]WHO, Haemoglobin concentrations for the diagnosis of anaemia and assessment of severity.
3. [3]BIPM, The International System of Units (SI Brochure), 9th ed., version 3.01, coherent derived units and quantity equations.