Hematocrit to Hemoglobin Ratio Calculator (rule of three check)

Understanding the hematocrit to hemoglobin ratio calculator — concept and principle

This calculator checks a blood count with the "rule of three": hematocrit in percent is usually about three times the hemoglobin in g/dL. It shows the ratio, the values each one predicts for the other, and the mean corpuscular hemoglobin concentration (MCHC). Students and lab staff use it to cross-check results.

The rule of three: with the default inputs the result is MCHC 32.9 g/dL (within 32–36 → rule fits).

How it is calculated

Ratio = hematocrit (%) ÷ hemoglobin (g/dL)

Estimated hemoglobin = hematocrit ÷ 3; estimated hematocrit = hemoglobin × 3

MCHC (g/dL) = hemoglobin ÷ (hematocrit ÷ 100)

Hemoglobin in g/L is divided by 10 to get g/dL.
The rule fits when the MCHC is within 32–36 g/dL.

The principle

Hematocrit is the share of blood volume taken up by red cells; hemoglobin is the amount of hemoglobin per volume of blood. Their quotient is the concentration of hemoglobin inside the red cells (MCHC), which is held in a narrow range of about 32–36 g/dL in normal cells. Since 100 ÷ 33 is about 3, hematocrit is roughly three times hemoglobin. When the cells carry less hemoglobin than usual, the ratio rises above 3.

Worked example

Default inputs: hemoglobin 13.5 g/dL, hematocrit 41%.

Ratio = 41 ÷ 13.5 = 3.04.
Estimated hemoglobin = 41 ÷ 3 = 13.7 g/dL; estimated hematocrit = 13.5 × 3 = 40.5%.
MCHC = 13.5 ÷ 0.41 = 32.9 g/dL.
32.9 is within 32–36 → Yes — MCHC within 32–36 g/dL.

Each point is the calculator re-run with only “Hemoglobin” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Hemoglobin	Hematocrit ÷ hemoglobin
3.38	12.15
6.75	6.07
10.1	4.05
13.5	3.04
16.9	2.43
20.2	2.02
27	1.52

How to read the result

Where does your result fall?

A ratio clearly above 3 (low MCHC) fits hypochromic red cells, as in iron deficiency or thalassaemia. A ratio below 3 (high MCHC) is unusual and may point to spherocytes or a sample problem such as lipaemia, haemolysis or cold agglutinins. The rule is a quick plausibility check, not a substitute for measured indices.

Common mistakes

Mixing g/L and g/dL for hemoglobin.
Entering hematocrit as a fraction (0.41) instead of a percentage (41).
Using the estimates in place of measured values.

Keep in mind: This is not a diagnosis. Abnormal blood counts should be interpreted by a doctor with the full blood picture.

Frequently asked questions

Why is hematocrit about three times hemoglobin?

Because normal red cells contain about 33 g/dL of hemoglobin, and 100 ÷ 33 ≈ 3.

What does a low MCHC mean?

Red cells are paler than normal, most often because of iron deficiency.

Can the rule be used in newborns?

Newborn values differ and change quickly; use age-specific reference ranges.

Sources: Wintrobe's Clinical Hematology (red cell indices and MCHC reference range)

Checked 9 Nov 2026. MCHC = Hb ÷ (Hct/100) and reference range 32–36 g/dL as given in “Red blood cell indices” (WikiProject Medicine / mdwiki, 2024 edition); the rule of three follows from that MCHC.

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